Appendage mountable electronic devices conformable to surfaces

ABSTRACT

Disclosed are appendage mountable electronic systems and related methods for covering and conforming to an appendage surface. A flexible or stretchable substrate has an inner surface for receiving an appendage, including an appendage having a curved surface, and an opposed outer surface that is accessible to external surfaces. A stretchable or flexible electronic device is supported by the substrate inner and/or outer surface, depending on the application of interest. The electronic device in combination with the substrate provides a net bending stiffness to facilitate conformal contact between the inner surface and a surface of the appendage provided within the enclosure. In an aspect, the system is capable of surface flipping without adversely impacting electronic device functionality, such as electronic devices comprising arrays of sensors, actuators, or both sensors and actuators.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/853,770 filed Mar. 29, 2013, which claims benefit to U.S. ProvisionalPatent Application Nos. 61/794,004 filed Mar. 15, 2013, 61/636,527 filedApr. 20, 2012 and 61/618,371 filed Mar. 30, 2012, each of which areincorporated by reference to the extent not inconsistent herewith.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with government support under CMMI-0328162 andawarded by the National Science Foundation, and DE-FG02-07ER46471 andDE-FG02-07ER46453 awarded by the Department of Energy. The governmenthas certain rights in the invention.

BACKGROUND OF INVENTION

Physiological measurement and stimulation techniques that exploitinterfaces to the skin have been of interest for many years. Despitemuch progress over this time, nearly all associated device technologiescontinue to rely on conceptually old designs. Typically, small numbersof bulk electrodes are mounted on the skin via adhesive tapes,mechanical clamps/straps and/or penetrating needles, often mediated byconductive gels, with terminal connections to separate boxes that housecollections of rigid circuit boards, power supplies and communicationcomponents. These systems have many important capabilities, but they arepoorly suited for practical application outside of research labs orclinical settings, due to difficulties in establishing long-lived,robust electrical contacts that do not irritate the skin, and inachieving integrated systems with overall sizes, weights and shapes thatdo not cause discomfort during prolonged use.

Recently, a number of patents and publications have disclosed flexible,resilient and implantable electrode arrays. For example, U.S. PatentApplication Publication US 2007/0043416 discloses an implantableflexible elastic support with a plurality of electrodes held in contactwith a target tissue. Similarly, International Patent ApplicationPublication WO 98/49936 discloses a resilient electrode array forsensing signals associated (mapping) and ablating heart tissue. U.S.Pat. No. 5,678,737 discloses an electrophysiology mapping system fordisplaying a 3D model of epicardial and endocardial surfaces withdynamic display of potential distribution data.

U.S. Patent Application Publication US 2003/0149456 discloses amulti-electrode cardiac lead adapter which incorporates a multiplexingcircuit allowing for control by a conventional single lead cardiacpacing pulse generator. Similarly, U.S. Patent Application PublicationUS 2006/0173364 discloses a multichannel electrophysiology acquisitionsystem which utilizes a digital multiplexing circuit build on aconventional integrated circuit. U.S. Pat. No. 6,666,821 discloses animplantable sensor array system with an associated protective memberwhich prevents the sensors from interacting with the surroundingenvironment until it is disabled.

International Application Publication WO 2009/114689 and U.S. PatentPublication No. 2013/0041235, each of which are individually herebyincorporated by reference in its entirety, discloses flexible andscalable sensor arrays for recording and modulating physiologicactivity. US Patent Application Publication Nos. US 2008/0157235, US2008/0108171, US 2010/0002402 and U.S. Pat. No. 7,557,367 issued Jul. 7,2009, all of which are hereby incorporated by reference in theirentireties, disclose multilayer stretchable, foldable and printablesemiconductor devices.

There is a need in the art for high-fidelity, robust and reliableelectronics on surfaces that are capable of accommodating any type ofcurved surface, including highly complex shapes such as those associatedwith moving fingers. One difficulty with providing electronics tointeract with such complex surface shapes is that it can be difficultyto reliably provide electronics in a correspondingly complex surfaceshape so as to achieve good interaction between the electronics and thecomplex surface shape over a large contact area. Provided herein arevarious devices and methods that address this aspect.

SUMMARY OF THE INVENTION

Provided herein are devices and methods related to ultrathin flexibleand stretchable electronics that may be incorporated with flexiblesurfaces to permit electrical interfacing with a range of surfaces andsurface shapes, including highly irregular shaped surfaces that maychange shape over time. In an embodiment, the invention is an electronicdevice having an enclosure that is shaped to cover and conform to acurved surface, including a fully three-dimensionally varying surfacehaving complex shapes with at least one surface that faces anothersurface, such as an appendage of a person that moves and changes shapewith movement. Alternatively, the appendage may be part of a non-livinginstrument or inanimate object, such as a remote sensing device orrobotic instrument.

In an aspect, the invention provides an appendage mountable electronicsystem, the system comprising: (i) a flexible or stretchable substratehaving an inner surface and an outer surface, wherein the inner surfacedefines an enclosure capable of receiving an appendage having a curvedsurface; and (ii) a flexible or stretchable electronic device comprisingone or more sensors, actuators or both supported by the inner surface orthe outer surface of the flexible or stretchable substrate; the sensors,actuators or both comprising one or more inorganic semiconductorcomponents, one or more metallic components, or one or more inorganicsemiconductor components and one or more metallic components; wherein atleast a portion of the inorganic semiconductor components, metalliccomponents or both has a thickness less than or equal to 500 microns;wherein the flexible or stretchable substrate and the electronic deviceprovide a net bending stiffness of the system low enough such that theinner surface of the substrate is capable of establishing conformalcontact with a surface of the appendage provided within the enclosure.In an embodiment, for example, the appendage is a hand, a finger, afinger-tip, a skull, a foot, a toe, a leg, a torso, or any portionthereof. In an embodiment, for example, the system of the inventioncomprises an instrumented glove for covering a hand or an instrumentedfinger-tube for covering a finger or finger-tip, such as a medical glovefor surgery. In an embodiment, for example, the system of the inventioncomprises a human-machine interface system. In an embodiment, forexample, the system of the invention comprises a device for roboticmanipulation.

In an embodiment, for example, the flexible or stretchable substrate andthe electronic device provide the net bending stiffness of the systemless than or equal to 1×10⁸ GPa μm⁴. In an embodiment, for example, thenet bending stiffness of the device is low enough such that the one ormore sensors, actuators or both supported by the inner surface of thesubstrate are capable of establishing conformal contact with the surfaceof the appendage provided within the enclosure. In an embodiment, forexample, the flexible or stretchable substrate and the electronic deviceprovide a net flexural rigidity of the system less than or equal to1×10⁻⁴ Nm. In an embodiment, for example, the substrate is a flexiblesubstrate and the electronic device is a flexible electronic device. Inan embodiment, for example, the substrate is a stretchable substrate anddevice is a stretchable electronic device. In an embodiment, forexample, the system is characterized by a neutral mechanical plane andwherein at least a portion of the one or more inorganic semiconductorcomponents, or the one or more metallic components or both arepositioned proximate to the neutral mechanical plane. In an embodiment,a strain-sensitive material, including the material having a mechanicalproperty that is most sensitive to an applied strain, is positionedcoincident or, alternatively, proximate to, the neutral mechanicalplane.

Any of the systems provided herein may have from between about 2 toabout 1000 of sensors, actuators or both. In an embodiment, theelectronic device comprises at least 3 different types of sensors,actuators or both. In an aspect, the one or more sensors, actuators orboth are provided in an open mesh geometry.

Any of the systems are optionally described in terms of a footprintsurface area of the one or more sensors, actuators or both. In anembodiment, the footprint surface area is selected from the range of 0.5cm² to 100 cm². In an aspect, the footprint surface area corresponds toan array of sensors, actuators or both, wherein individual sensors oractuators have relatively small individual footprints, but the membersof the array are spread to provide a desired footprint, including largerarea footprints. Accordingly, depending on the application of interest,such as the surface area of the appendage being interfaced with, thefootprint area is correspondingly selected. In this manner, a finger-tipappendage system may have a footprint surface area in the 0.5 cm² toabout 2 cm², whereas for an arm, leg, or head, the footprint surfacearea may be desirably larger such as 10 cm² to 100 cm².

The systems provided herein are compatible with a large range ofsensors, depending on the application of interest. Examples include oneor more sensors selected from the group consisting of an electrode, atactile sensor, a strain gauge, a capacitance sensor, a temperaturesensor, a pressure sensor, a motion sensor, a position sensor, adisplacement sensor, an acceleration sensor, a force sensor, a chemicalsensor, a pH sensor, a capacitive sensor, an optical sensor, aphotodetector, a hydration sensor, an imaging system and any arrays andcombinations thereof.

The systems provided herein are compatible with a large range ofactuators, depending on the application of interest. Examples includeone or more actuators selected from the group consisting of anelectrotactile stimulator, an electrode, a heat source (thermalactuator), a piezoelectric element, an acoustic element, a source of RFenergy, a magnetic actuator, a source of electromagnetic radiation, alaser, a light source, a light emitting diode and arrays, and any arraysand combinations thereof.

In an embodiment, at least a portion of the sensors, actuators or bothare supported by the inner surface of said flexible or stretchablesubstrate and at least a portion of the sensors, actuators or both aresupported by the outer surface of the flexible or stretchable substrate.In an embodiment, an electronic device may be supported by bothsurfaces, such as a pressure sensor having aligned and paired electronicdevices on both the internal and external surface that communicate witheach other to provide an output that varies with separation distancebetween the electronic surfaces, such as by an applied pressure thatchanges thickness of a substrate that is elastomeric. In this manner,the devices may be electrodes that provide a measure of capacitance, aheat source and sensor that provide a measure of temperature, an opticalsource and optical detector that provides a measure of a light property,such as optical intensity. The common aspect of these systems is thatthe output of the device depends on substrate thickness between thedevices, which in turns depends on the applied pressure or force. Inthis manner, the system provides a unique platform for pressure or forcemeasurement with an external surface.

In an embodiment, the electronic device comprises a plurality ofelectro-tactile stimulators provided in an array and supported by saidthe surface of the substrate for electrically stimulating an appendagein the enclosure. In an aspect, the functional electronic devicecomprises a multiplexed array of said electrotactile stimulators. In anaspect, the electro-tactile stimulators of the array are electricallyinterconnected via a network of serpentine electrical interconnects.

In an aspect, any of the electro-tactile stimulators provided hereincomprise a thin film metal structure having an inner region surroundedby an outer region, wherein a gap is provided between the inner regionand the outer region. Such regions are optionally described in term oftheir dimensions. Examples include an inner region having lateraldimensions selected from the range of 10 μm to 1000 μm, an outer ringhaving lateral dimensions selected from the range of 10 μm to 5000 μmand a gap having lateral dimensions selected from the range of 10 μm to1000 μm.

In an embodiment, the inner region is a conductive disk-shaped electrodeand the outer region is a conductive ring-shaped electrode positionedconcentric with said disk-shaped electrode.

In an embodiment, the electronic device comprises a plurality of tactilesensors provided in an array and supported by the outer surface, innersurface, or both the outer and inner surface of the substrate. In anaspect, the electronic device comprises a multiplexed array of tactilesensors. Paired electronic devices aligned but on opposite elastomericsubstrate surfaces provide one means for measuring a pressure or forceexerted by or against any of the systems provided herein.

In an embodiment, the tactile sensors of the array are electricallyinterconnected in independently connected via a network of serpentineelectrical interconnects.

In an aspect each of the tactile sensors comprises a thin film metalstructure having lateral dimensions selected from the range of 100 μm to5000 μm. In one example, the thin film metal structure of the tactilesensors is a conductive disk-shaped electrode.

In another embodiment the electronic device comprises one or moretactile sensors supported by the outer surface and one or moreelectro-tactile stimulators supported by the inner surface, wherein oneor more tactile sensors are in electrical communication with one or moreelectrotactile stimulators such that an output from the one or moretactile sensors is provided to the one or more electrotactilestimulators to electrically stimulate the appendage in proportion to thetactile sensor output. In one aspect, the inner surface and outersurface arrays are spatially aligned. “Spatially aligned” refers to anoutput from the sensor array that spatially varies, with the magnitudeof sensor output that varies with position of the sensor, and thecorresponding stimulation to the appendage that correspondinglyspatially varies in accordance with the spatially varying output fromthe sensors.

In an aspect, electronic device comprises a plurality of electrodes,each electrode comprising an inner disk having a diameter that is lessthan 1 mm; and an outer ring that surround the inner disk, wherein theinner disk and outer ring are concentrically positioned relative to eachother, with a separation distance between the inner disk and outer ringselected from a range that is greater than or equal to 100 μm and lessthan or equal to 500 μm.

As desired, any of the systems optionally further comprise one or moreadditional electronic components supported by the inner surface, theouter surface or both; the additional electronic components selectedfrom the group consisting of a sensor, an actuator, a power source, awireless power source, a photovoltaic device, a wireless transmitter, anantenna, a nanoelectromechanical system, a microelectromechanical systemand arrays and any combinations thereof. In an aspect, the one or moreadditional electronic components comprise a strain gauge, such as astrain gauge comprising one or more semiconductor nanomembranes.

In an embodiment, each semiconductor nanomembrane independently haslateral dimensions selected from the range of 1 μm to 10 mm and athickness selected from the range of 100 nm to 100 μm.

In an aspect, the strain gauge comprises a plurality of at least threeelectrically connected semiconductor nanomembranes.

In an aspect, the semiconductor nanomembranes are electricallyinterconnected via a network of serpentine electrical interconnects.

In an embodiment, any of the systems provided herein comprise one ormore inorganic semiconductor components, such as each of the one or moreinorganic semiconductor components independently comprising apolycrystalline semiconductor material, single crystalline semiconductormaterial or a doped polycrystalline or single crystalline semiconductormaterial.

In an aspect, each of the one or more inorganic semiconductor componentsindependently comprises a single crystalline semiconductor material. Inan aspect, each of the one or more inorganic semiconductor componentsindependently has a thickness that is less than or equal to 100 μm. Inan aspect, each of the inorganic semiconductor components of theelectronic device have a thickness selected from the range of 50nanometers to 100 μm. In an aspect, each of the inorganic semiconductorcomponents of the electronic device has a net flexural rigidity lessthan or equal to 1×10⁻⁴ Nm, a Young's modulus selected from the range of0.5 MPa to 10 GPa, a net bending stiffness less than or equal to 1×10⁸GPa μm⁴.

In an embodiment, each of the one or more inorganic semiconductorcomponents independently comprises a semiconductor nanomembranestructure, such as a nanomembrane structure that is a diode electroniccomponent.

In another aspect, any of the systems provided herein comprise one ormore metallic components. In an aspect, the one or more metallicconductor components comprise a plurality of electrodes provided in anarray.

In an embodiment, any of the metal electrodes provided herein, such aswithin an array, are described in terms of a thickness. In an aspect,the electrodes in an array independently have a thickness less than orequal to 100 μm, or selected from the range of 50 nanometers to 100 μm.In an embodiment, the number of electrodes in an electrode array isselected from a number that is between 10 to 10,000 electrodes.

In an aspect, the electrodes of the array are electricallyinterconnected via a network of serpentine electrical interconnects.

In an embodiment, any of the systems provided herein have the one ormore sensors, actuators or both of the electronic device comprises astretchable or flexible electrode array comprising a plurality ofelectrodes, multiplex circuitry and amplification circuitry. In anaspect, the stretchable or flexible electrode array comprises aplurality of electrode unit cells, such as 50 or more electrode unitcells. Optionally, adjacent electrode unit cells of the electrode arrayare further described in terms of a separation distance, such asadjacent unit cells separated from each other by a distance less than orequal to 50 μm, or a range between 500 nm and 50 μm. In an embodiment,the electrode unit cells of the electrode array are supported by an areaof the flexible or stretchable substrate ranging from 10 mm² to 10,000mm².

In an aspect, each electrode unit cell of the electrode array comprisesa contact pad, amplifier and multiplexer, wherein the contact padprovides an electrical interface to the tissue and is in electricalcommunication with the amplifier and multiplexer. In an embodiment, theamplifier and multiplexer of the unit cell comprises a plurality oftransistors.

Any of the one or more metallic conductor components herein comprise aplurality of stretchable electrical interconnects. Optionally, thestretchable electrical interconnects are at least partiallyfree-standing or provided in a tethered geometry. Optionally, thestretchable electrical interconnects have a curved geometry. Optionally,the electrical interconnects have a serpentine configuration.Optionally, the stretchable electrical interconnects electricallyconnect rigid device islands comprising at least a portion of the one ormore one or more inorganic semiconductor components, one or moremetallic components, or one or more inorganic semiconductor componentsand one or more metallic components.

In an aspect, at least a portion of the rigid device islands eachindependently comprise a single crystalline inorganic semiconductorstructure, or a single crystalline semiconductor nanomembrane.

In an aspect, the rigid device islands comprise the one or more sensors,actuators or both, such as sensors or actuators selected from the groupconsisting of: an electrode, a tactile sensor, a strain gauge, acapacitance sensor, a temperature sensor, a pressure sensor, a motionsensor, a position sensor, a displacement sensor, an accelerationsensor, a force sensor, a chemical sensor, a pH sensor, a capacitivesensor, an optical sensor, a photodetector, an imaging system, anelectrotactile stimulator, an electrode, a heat source, a piezoelectricelement, an acoustic element, a source of RF energy, a magneticactuator, a source of electromagnetic radiation, a laser, a lightemitting diode and arrays and any arrays and combinations thereof.

Any of the systems provided herein may have at least a portion of theflexible or stretchable electronic device supported by either the outersurface, by the inner surface of the flexible or stretchable substrate,or by both surfaces. In an aspect, the inner surface and outer surfaceare interchangeably flippable without substantial degradation of afunctionality parameter of the one or more sensors, actuators or bothsupported by the inner surface or the outer surface of the flexible orstretchable substrate.

For example, a system comprising an array of actuators, sensors, oractuators and sensors, is interchangeably flippable between inner andouter and outer and inner configurations without substantial degradationof a functionality parameter of the array of actuators, sensors, oractuators and sensors. In an aspect, the flipping facilitates placementof electronic devices on an inner surface that is otherwise notaccessible or amenable to conventional printing techniques. In anembodiment, the outer surface that supports the electronic device isflipped, so that after flipping the functional electronic devicesupported by the outer surface is the functional electronic devicesupported by the inner surface. In an embodiment, the functionalelectronic device is an array of electrotactile stimulators, and atleast 90% of the electrotactile stimulators remain functional afterflipping from an outer facing surface to an inner facing surfacegeometry.

In an aspect, the flexible or stretchable substrate has a closed tubegeometry. In an embodiment, the closed tube geometry has one accessopening or two access openings.

In an aspect, the enclosure has cross sectional dimensions selected fromthe range of 5 mm to 1000 cm. Depending on the application of interest,the cross sectional dimensions are appropriately selected. For example,finger-tip electronics may have a smaller cross sectional dimension thana torso or a head electronics system, which may be smaller than a remotesensing vehicle or instrument surface connected thereto.

In an embodiment, any of the flexible or stretchable substrates providedherein is an elastomeric substrate.

In an aspect, the flexible or stretchable substrate is a polymer, aninorganic polymer, an organic polymer, a plastic, an elastomer, abiopolymer, a thermoset, rubber, or any combination of these. In anaspect, the flexible or stretchable substrate is PDMS, parylene,polyimide, or silicone such as Ecoflex® (Smooth-On, Inc.) silicone. Inan aspect, the flexible or stretchable substrate is a biocompatiblematerial or a bioinert material.

In an embodiment, the flexible or stretchable substrate has an averagethickness selected over the range of 0.25 μm to 10,000 μm, including anysub-combination thereof, such as between about 1 μm and 5 mm, or about 1mm.

In an aspect, the flexible or stretchable substrate has a substantiallyuniform thickness supporting the electronic device or has a thicknesssupporting the electronic device that varies selectively along one ormore lateral dimensions. In this context, “substantially uniform” refersto a substrate at rest having a thickness that varies less than about10%, less than about 5% or less than about 1%. Alternatively,substantially uniform may refer to a substrate that has received anappendage in the enclosure, having a thickness that that varies lessthan about 10%, less than about 5% or less than about 1%. Optionally,substantially uniform refers to a statistical parameter, such as astandard deviation or standard error of the mean of an average thicknessthat is within about 10%, 5% or 1% of the average thickness over aselected portion of the substrate, or over the entire substrate surfacearea.

In an embodiment, the flexible or stretchable substrate is a flexible orstretchable mesh structure. In an embodiment, at least a portion of theelectronic device has a mesh structure. Examples of mesh structuresinclude open mesh geometries where a substantial portion of the relevantis open space or void, such as for longitudinally aligned interconnectswhich may be curvy but have a general alignment direction. Similarly,longitudinally arranged strips of substrate may be provided such as toprovide additional breathability to an appendage to which the system ismounted. Alternatively, the substrate may have perforations or passages.This mesh aspect may be defined in terms of relative amount of openspace compared to the perimeter-defined substrate footprint, such asbetween about 10% to 90%, and any subranges thereof, such as between 20%to 80%, 30% to 70%, depending on the application of interest.

In an aspect, the flexible or stretchable substrate has an averageYoung's modulus selected over the range of 0.5 KPa to 10 GPa and/or afracture strain greater than or equal to 500%, such as between about500% and 900%.

Any of the systems provided herein may further comprise a barrier layerat least partially encapsulating at least a portion of the functionaldevice. For example, the barrier layer may limit a net leakage currentfrom the electronic device to an amount which does not adversely affecta material in contact with the system or limits a heat transfer from theelectronic device to an amount which does not adversely affect amaterial in contact with the system. This can be particularly beneficialin the context of biological systems that may be adversely affected byelectrical or thermal leakage, such as an biological tissue covering anappendage within the enclosure.

The barrier layer may also substantially prevent passage of an externalfluid to at least a portion of the electronic device. This may bebeneficial to maintain electronic device functionality, robustness, andlong-term wear characteristics.

In an embodiment, the barrier layer is a polymer, an inorganic polymer,an organic polymer, a plastic, an elastomer, a biopolymer, a thermoset,rubber or any combination of these. In an embodiment, the barrier layeris PDMS, parylene, polyimide, or Ecoflex®. In an embodiment, the barrierlayer comprises a composition that corresponds to the flexible orstretchable substrate.

In an aspect, the barrier layer has an average thickness selected fromthe range of 1 μm to 100 μm, an average modulus selected over the rangeof 0.5 KPa to 10 GPa. Optionally, the barrier layer is described by aratio of the average thickness of the barrier layer to the averagethickness of the flexible or stretchable substrate, such as a ratio thatis selected over the range of 0.01 to 1. Depending on the specificapplication, the barrier layer is positioned as desired. Examples ofpositions include between otherwise adjacent device layers and/orbetween a device layer and the surrounding environment such as theappendage, air, or an external surface. In an aspect, the barrier layerhas a mesh structure.

In an embodiment, the system further comprises one or more stretchableinterconnects that electrically connect at least a portion of said oneor more sensors, actuators or both. Such stretchable interconnects maybe configured to impart stretchability and/or flexibility to the system.Any of the one or more stretchable interconnects comprises anelectrically conductive metal provided in a bent configuration.

Bent configuration is used broadly and may include a nanowire in aserpentine configuration. The nanowire may have a rectangularcross-section, with a thickness selected from the range of 50 nm to 1 μmand a width that is selected from the range of 10 μm to 1 mm. Theserpentine configuration may be meandering undergoing a plurality ofdirectional changes relative to an average longitudinal directiondefined by a straight line between the interconnect ends. In an aspect,the serpentine configuration is characterized by an average radius ofcurvature selected from the range of 100 μm to 10 mm.

In an aspect, the system comprises a plurality of interconnects arrangedin at least two interconnect layers, with adjacent interconnect layersseparated by a barrier layer that is an electrically insulativeelastomeric layer. This configuration facilitates compact overlyinginterconnect wiring. In an aspect, the electronic devices comprise rigiddevice islands electrically connected to at least one interconnect,wherein the interconnect bent configuration accommodates stresses frombending and stretching of the thin elastomeric substrate. In an aspect,the bending and stretching stresses are from flipping the inner andouter surfaces of the flexible or stretchable substrate.

In an aspect, the system has a neutral mechanical plane (NMP), that ispositioned at a depth that corresponds to a depth of a strain-sensitivecomponent. For example, the NMP may run along a surface defined by orwithin the strain-sensitive components, such as a strain sensitivecomponent that is a semiconductor or metal material. Optionally, NMPpositioning is by providing substrate or barrier layers, including byvarying the thickness of those layers.

In an aspect, at least a portion of the one or more inorganicsemiconductor components, one or more metallic components or both areprintable structures. In an embodiment, at least a portion of the one ormore sensors, actuators or both are assembled on the flexible orstretchable substrate via transfer printing. In an embodiment, at leasta portion of the one or more sensors, actuators or both are assembled onsaid flexible or stretchable substrate via microtransfer printing, drycontact transfer printing, solution-based printing, soft lithographyprinting, replica molding, or imprint lithography.

In an embodiment, the enclosure has an interior volume and at least oneopening for receiving and covering an appendage. In an aspect, theenclosure interior volume that is greater than or equal to 1 cm³ andless than or equal to 10,000 cm³.

In an aspect, the enclosure has a shape, such as a substantiallycylindrical or hemispherical shape. In an aspect the enclosure is shapedto receive a hand, a finger, a finger-tip or any portion thereof.

In an embodiment, the enclosure has one or two access openings forreceiving the appendage, such as one opening to receive an appendagethat is a finger or a head portion, or two openings to receive an arm,leg, or torso, wherein a portion of the appendage extends through theenclosure first and second access openings.

In an aspect, the flexible or stretchable substrate wraps around theappendage under a longitudinally-directed tension or is rolled over theappendage under a circumferentially-directed tension.

In an embodiment, the appendage is part of a living animal, such as afinger, an arm, a leg, a head, a torso, or any portion thereof.

In an aspect, any of the systems provided herein relate to first andsecond electronic devices supported by opposing surfaces, such as innerand outer surfaces, wherein the devices are in communication with eachother. Depending on the type of device, the communication ischaracterized by a parameter, such as an electrical parameter(capacitance) or thermal (temperature), that varies with substratethickness between the devices. Preferably, the substrate is elastomeric.In this manner, a pressure sensor is provided, wherein the communicationparameter depends on substrate thickness, which in turn depends on theapplied force or pressure exerted on the substrate.

In an aspect, the enclosure has a receiving dimension that is smallerthan a corresponding dimension of the appendage, wherein during use astrain in the flexible or stretchable substrate increases the receivingdimension to accommodate the appendage within enclosure withoutadversely impacting the flexible or stretchable electronic device. In anembodiment, the strain generates a contact force between the elastomericsubstrate and the appendage within the enclosure to establish andmaintain intimate and conformal contact between the flexible orstretchable electronic device supported by the substrate inner surfaceand a surface of the appendage. In an aspect, the strain is selectedfrom a range that is greater than or equal to 1% and less than or equalto 100%.

In an embodiment, the array of sensors, actuators or both, are describedin terms of a spatial density, such as a spatial density selected from arange that is between about 1 mm⁻² and 1 cm⁻².

In an aspect, any of the systems are multifunctional, wherein the innersurface supports a first array of actuators or sensors, and the outersurface supports a second array of sensors or actuators. In anembodiment, the first array comprises electrotactile stimulators tointerface with skin of a living animal in conformal contact with theelectronic devices of the first array, and the second array comprisestactile sensors to measure a physical parameter from tactile interactionwith an external surface. In an aspect, the tactile sensor comprisesopposing electrodes on the inner and the outer surfaces to measure acapacitance between the electrodes, wherein the capacitance varies withsubstrate thickness between the opposing electrodes.

In an aspect, the inner surface supports a first electronic device andthe outer surface supports a second electronic device, wherein theelectronic devices are in an opposed configuration and in communicationwith each other, wherein they form, for example, a pressure sensor. Inan aspect, the communication is electrical communication (capacitance)wherein an electrical property varies with substrate thickness betweenthe first and second opposed electronic devices. In an aspect, thedevices are in thermal communication, wherein a thermal property changeswith substrate thickness between the opposed electronic devices. In anaspect the devices are in mechanical communication (pressure or force).

In an embodiment, the first and second electronic devices are in thermalcommunication with each other. For example, one electronic device may bea heater and a second electronic device may be a thermal sensor, withthe heater placed on an inner or outer surface and the thermal sensor onthe opposite surface, wherein the heater can maintain a constanttemperature on its support surface. In this manner, the thermalcommunication between the heater and sensor is used to assess a pressureor force exerted against a substrate whose thickness varies depending onthe magnitude of the pressure or force applied against the substrate.Generally, with higher applied pressures, substrate thickness decreasesthereby increasing thermal conductivity from the heater to the sensorwhich is detected by an increase in the temperature detected by thethermal sensor. In an aspect, the heater is a resistive heater whosetemperature increases with increasing current, such as by electricallyconductive wires connected to a heating pad. In an aspect where theappendage is living tissue, preferably the heater is placed on the outersurface to avoid unwanted heating of the living tissue. Accordingly, thethermal sensor may be aligned with the heater on an inner surface. In anaspect, the system may be calibrated by the use of an unpaired thermalsensor to adjust for fluctuations in ambient temperature. Alternativelythe communication may be optically, between an optical source andoptical detector, wherein optical transmission varies as a function ofsubstrate thickness between source and detector.

In an aspect, a sensor is provided on the inner surface of any of thesystems described herein. The sensor or sensors may be one or more of athermal sensor to measure body temperature including as a measure ofbody core temperature, a hydration sensor to measure hydration levelsincluding as a measure of whole body hydration, or another sensor todetect a biological parameter of interest (e.g., pH, oxygenation level,etc.). Such measures are useful in providing warning about potentialrisk of an adverse event, such as heat-stroke or dehydration.

In an embodiment, the first and second electronic devices are inelectrical communication with each other, wherein change in substratethickness changes electrical capacitance or electrical resistancebetween the electronic devices. In this manner, pressure or force isdetermined by measuring capacitance between a pair of aligned electrodeson the inner and outer surfaces. In an aspect, the second array ofsensors generates an electrical output that is input to the first arrayof actuators, wherein the first array of actuators interface with theappendage surface that is skin of a user to provide information to theuser about the external surface. In this context, “information” refersto a property that is detected by the sensor, and so accordingly, can bea physical property such as contact force or pressure generated bysurface contact or a property inherent to an external surface, such astemperature, pH, hydration, or presence of a chemical or biologicalmaterial.

An example of an appendage mountable electronic system includes: (i) anelastomeric substrate having an inner surface and an outer surface,wherein the inner surface defines an enclosure capable of receiving anappendage having a curved surface; (ii) a first electronic devicesupported by the inner surface; (iii) a second electronic supported bythe outer substrate, wherein the first and second electronic devices arein an opposed configuration with respect to each other and separated bya thickness of the elastomeric substrate to form a functional pressuresensor whose output varies as a function of elastomeric substratethickness; wherein each of the first and second electronic devices maycomprise a thin electrically conductive material having a thickness lessthan 1 mm and a lateral dimension less than 5 mm and the elastomericsubstrate has a resting thickness that is less than 10 mm to for anoutput that is capacitance when an electrode is energized.

In another embodiment, the appendage mountable electronic systemcomprises: an elastomeric substrate having an inner surface and an outersurface, wherein the inner surface defines an enclosure capable ofreceiving an appendage having a curved surface, and the elastomericsubstrate has a resting thickness that is less than 10 mm; a firstelectronic device supported by the inner surface; a second electronicdevice supported by the outer substrate, wherein the first and secondelectronic devices are in an opposed configuration with respect to eachother and separated by a thickness of the elastomeric substrate to forma pressure sensor whose output varies as a function of elastomericsubstrate thickness; each of the first and second electronic devicescomprises one or more inorganic semiconductor components, one or moremetallic components, or one or more inorganic semiconductor componentsand one or more metallic components, having a thickness less than 1 mmand a lateral dimension less than 5 mm.

In an aspect, the system further comprises a first plurality ofelectrical interconnects to electrically connect each member of thearray of first electrodes and a second plurality of electricalinterconnects to electrically connect each member of the second array ofelectrodes, wherein the electrical interconnects are in a serpentineconfiguration. The electrical interconnects may be independentlyencapsulated by an encapsulation layer. A barrier layer may electricallyisolate the first plurality of electrical interconnects from the secondplurality of electrical interconnects. An applied pressure to theelastomeric substrate decreases substrate thickness between the pair ofelectrodes, thereby increasing the capacitance. Another example is firstand second electronic devices that are in thermal communication witheach other, wherein one of the electronic devices is a thermal sourceand the electronic device is a thermal detector that measures atemperature, and a change in elastomeric substrate thickness between thethermal source and the thermal detector changes the temperature measuredby the thermal detector.

The systems discussed herein are also referred to as an “appendagemountable electronic system” or “appendage conforming system”, and maycomprise a thin flexible and/or stretchable substrate having an innersurface and an outer surface. The substrate inner surface defines anenclosure for receiving a curved surface (e.g., an appendage surface),such as by covering and conformally contacting the surface associatedwith an appendage in the enclosure. Optionally, the substrate isdescribed in terms of a thickness, such as a thickness that is less than10 mm, a thickness that is less than 1 mm, a thickness that is less than500 μm, or a thickness selected over a range that is greater than orequal to 100 μm and less than or equal to 1 mm. Thickness may beselected based on the operating conditions and relevant application. Forexample, in applications having substantial surface abrasion, thesubstrate may be correspondingly thicker and/or have higher durabilitycharacteristics. A functional electronic device is supported by theelastic substrate inner surface or the elastic substrate outer surface.The functional electronic device comprises a device component that isone or more inorganic semiconductor components, one or more metalliccomponents, or one or more inorganic semiconductor components and one ormore metallic components. The functional electronic device, includingany device components thereof, is stretchable and bendable. Thefunctional electronic device, including any device components thereof,have a thickness, such as a thickness that is less than or equal to 10μm. The thin lay-out geometry of the devices and the properties of theelastomeric substrate provide a number of functional benefits in termsof the interaction between object surfaces and the electronic device,and also to facilitate certain unique transfer printing processes formaking any of the devices herein.

For example, the inner surface of the substrate may be visually and/orphysically inaccessible in that the three-dimensional shape of theenclosure is a closed surface that defines an interior volume. Such anenclosure, particularly if small, is difficult to access, making itdifficult to place functional electronic devices on the enclosuresurface. Although such an enclosure may have one or two openings, itstill may not be readily accessible for transfer printing of functionalelectronic devices, in comparison to an open enclosure having a free endthat may be used to open the enclosure to transfer printing. Theelastomeric substrate properties of the instant invention allow for thespecially configured functional electronic devices on an outer surfaceto be flipped so that functional electronic devices are on the innersurface defining the enclosure. This is achieved by the specialconfigured thin device component layouts and correspondingly thinfunctional electronic device, that can be substantially stretched, bent,and/or folded without adversely impacting device functionality.Accordingly, an aspect of the instant invention relates to an innersurface that is not physically accessible to conventional electronicdevice transfer printing processes. The outer surface of any of thesubstrates discussed herein, in contrast, faces away from the interiorand is visually and physically accessible with no or minimal appliedforce. For example, the outer surface may have invaginations that becomephysically accessible by a relatively straight-forward minimal forceapplication to stretch the substrate and remove invaginations or foldsover a desired region. Transfer printing functional electronic devicearrays to the outer surface, followed by substrate surface flipping,facilitates placement of functional electronic device and arrays inextremely confined interior volumes and enclosures not otherwiseaccessible to conventional transfer printing techniques.

In an embodiment, any of the substrates in any of the devices andmethods provided herein, has an inner and outer surface that areinterchangeably flippable without substantial degradation of afunctionality parameter of the functional electronic device supported bythe inner surface or the outer surface. In this embodiment, it does notmatter which surface supports the functional electronic device, as thesubstrate surfaces can be readily flipped so that an outward facingelectronic device can be flipped inward by flipping the substratesurfaces. Similarly an inward facing electronic device can be flippedoutward by flipping the substrate surfaces. Accordingly, in an aspect,the elastomeric substrate material and the attached functionalelectronic devices, are selected so as to have appropriate physicalcharacteristics to allow flipping without adversely impacting thesubstrate integrity or device functionality. For example, the materialmay have a relatively low modulus, such as less than 1 MPa, less than500 kPa, less than 100 kPa, or selected from a range that is greaterthan or equal to 10 kPa and less than or equal to 200 kPa. Similarly,the substrate may have a relatively high fracture strain, such as afracture strain that is greater than or equal to about 200%, 500%, 800%,or that is selected from a range that is greater than or equal to 400%and less than or equal to 1,200%. In an aspect, including forinterfacing with a user's skin, the substrate may be a siliconematerial, such as Ecoflex® silicone (Shore 00-30 hardness (Smooth-On,Inc.)).

In one aspect, any of the electronic devices provided herein comprise anarray of functional electronic devices. In one embodiment, thefunctional electronic devices are sensors, actuators, or both sensorsand actuators. For example, a sensor may provide information about aphysical parameter related to the electronic device, such as sensormotion, velocity, acceleration, or about a physical parameter associatedwith a surface in which the electronic device physically contacts, e.g.,pressure, force, temperature, electric potential, conductivity,hydration, moisture, electromagnetic radiation, or for any parameterthat a sensor is capable of measuring. An actuator, in contrast,functions to provide a signal or stimulus to a surface. Optionally, theplurality of actuators may be controlled by a plurality of sensors, suchas actuators on an inner surface and sensors on either the outer surfaceor the outer surface of another substrate. In this manner, virtualreality systems are provided, such as a user that “feels” what anothersurface “feels” like without actually touching the surface, such as by aremote controlled instrument or robotic device having a surface coveredwith any of the devices provided herein. Alternatively, amulti-functional device, such as a glove, may have sensors on the outersurface to sense a parameter which is then transmitted to a stimulatoron the inner surface in conformal contact with the user skin. In thismanner, information about a condition outside the glove is detected by auser via the stimulator on the inner surface.

One manner in which the ability to flip and/or stretch substratesurfaces to accommodate shaped surfaces, even highly irregular shapes,without sacrificing device functionality is by specially constructingand packaging the electronic layout and geometry so that rigid materialsmost susceptible to fracture are insulated from high stresses. Forexample, flexible and stretchable interconnects may be incorporated intothe functional electronic devices and positioned so as to accommodatebending and flexing stresses, thereby insulating rigid or brittlematerials from unduly high stresses. The interconnects electricallyconnect a functional electronic device, including multiple functionalelectronic devices, that may be configured as rigid device islands. Inan embodiment, the flexible and stretchable electrical interconnectcomprises an electrically conductive metal in a bent configuration.Examples of bent configurations include wavy geometry (see, e.g., U.S.Pat. No. 7,622,367 (38-04A)), buckle geometry (see, e.g., U.S. Pat. No.8,217,381 (134-06)), and/or serpentine configurations (see, e.g., U.S.Pat. Pub. 2010/0002402 (213-07); PCT Pub. WO2011/084450 (126-09WO); U.S.Pat. Pub. 2013/0041235 (29-11)).

Optionally, an interconnect comprises a nanowire in a serpentineconfiguration. High flexibility and bendability is achieved particularlyby providing interconnect cross-sectional dimensions that are smallrelative to the more rigid components that the interconnects connect.For example, the nanowire can have a rectangular cross-section, with athickness selected from a range that is greater than or equal to 50 nmand less than or equal to 1 μm, and a width that is selected from arange that is greater than or equal to 1 μm and less than or equal to 1mm. In an aspect, the serpentine configuration is characterized by anaverage radius of curvature, such as selected from a range that isgreater than or equal to 100 μm and less than or equal to 10 mm.

In an aspect, the electronic device comprises a plurality ofinterconnects arranged in at least two interconnect layers, withadjacent interconnect layers separated by a barrier layer that is anelectrically insulative elastomeric layer, thereby providing compactwiring with overlying interconnects.

The electrical interconnects are particularly advantageous inembodiments wherein the functional electronic devices are relativelyrigid, such as being made from relatively brittle components, includingsemiconductor components such as thin layers. In an aspect, thefunctional electronic devices comprise rigid device islands that areelectrically connected to at least one interconnect. In this aspect, theinterconnect bent configuration accommodates stresses from bending andstretching of the thin elastomeric substrate, thereby isolating therigid device islands from applied stresses. In an aspect, the bendingand stretching stresses are from flipping the inner and outer surfacesof the thin elastomeric substrate.

Any of the electronic devices provided herein may comprise an array offunctional electronic devices characterized by a total number offunctional electronic devices, such as a number selected from a rangethat is greater than or equal to 2 and less than or equal to 1000. In anaspect, the number is from between about 4 and 100. In an aspect, thenumber is from between about 4 and 20. In an aspect, any of the arraysdescribed herein are further defined in terms of a footprint area,wherein the footprint area is the surface area covered by the array, andcan be defined as the outermost portion of individual devices within thearray. Accordingly, based on the number of functional electronic devicesand the footprint area, a spatial density is determined. Forapplications requiring fine spatial resolution, there may be as many asabout 1 to 10 devices per mm². For other applications where fine spatialresolution is not necessary, the devices may be more sparselydistributed, such as 1 to 10 devices per cm².

In an aspect, the functional electronic device comprises a multiplexedarray of electrotactile stimulators for interfacing with a curvedsurface, wherein the curved surface corresponds to living tissue.

In an embodiment, any of the electronic devices provided herein are partof a human-machine interface, such as an instrumented glove or a medicalglove for surgery. The electronic devices are readily used in otherapplications, including an array of force or pressure sensors formeasuring force or pressure exerted against a surface. Such anapplication can provide a highly accurate understanding of, for example,forces exerted against a surface and correspondingly provide warnings oralarms if threshold values are exceeded. This can occur, for example, onany biological surface.

In an aspect, the inorganic semiconductor components and/or the metallicconductor components independently comprise one or more thin filmstructures having a thickness that is less than or equal to 1 μm.

In an embodiment, the electronic device comprises one or more inorganicsemiconductor components, such as inorganic semiconductor componentsindependently comprising a nanomembrane structure, a polycrystallinesemiconductor material, single crystalline semiconductor material or adoped polycrystalline or single crystalline semiconductor material.

In an aspect, the device has a neutral mechanical plane (NMP), whereinthe NMP is positioned at a depth that corresponds to the inorganicsemiconductor position within the device, such as an inorganicsemiconductor that is a nanomembrane. Such NMP positioning furtherassists in device tolerance to bending and stretching stresses, such asoccurs during flipping of the substrate inner and outer surfaces.

In an aspect, the device comprises one or more metallic conductorcomponents, such as a metallic conductor component that is an electricalinterconnect having a curved geometry. The curved geometry may be atleast partially free-standing. The curved geometry may comprise aserpentine configuration, with the bending either in plane, out ofplane, or a combination thereof. In an embodiment, electricalinterconnects electrically connect rigid device islands. In an aspect,rigid device islands comprise an inorganic semiconductor, such as asilicon nanomembrane.

In an aspect, the rigid device islands correspond to positions ofsensors or actuator components that tend to be strain-sensitive due tovarious parts that are relatively brittle and susceptible to physicalfracture. In an aspect, the sensors or actuators are electrotactiledevices, motion sensors, pressure sensors, pressure actuators, thermalsensors, thermal sources, or a combination thereof the configuration maybe described as a mesh geometry, in that the curved interconnects areconfigured to accommodate stresses not otherwise well-tolerated by arigid device island.

As described, the functional electronic device can be supported by thesubstrate outer surface or by the substrate inner surface, particularlyin view of the embodiment where the substrate is flippable. In anaspect, the outer surface that supports the functional electronic deviceis flipped, so that after flipping the functional electronic devicesupported by the outer surface is the functional electronic devicesupported by the inner surface. In an aspect, after flipping at least90% of the functional electronic devices on the inner surface remainfunctional after flipping from an outer surface facing to an innerfacing surface geometry. In this manner, the enclosure defined by theinner surface actually corresponds to a substrate surface that wasoriginally an outer surface.

In an embodiment, for example, at least a portion of the one or moreinorganic semiconductor components, one or more metallic components orboth are printable structures. In an embodiment, for example, at least aportion of the one or more sensors, actuators or both are assembled onsaid flexible or stretchable substrate via transfer printing. In anembodiment, for example, at least a portion of said one or more sensors,actuators or both are assembled on said flexible or stretchablesubstrate via microtransfer printing, dry contact transfer printing,solution-based printing, soft lithography printing, replica molding, orimprint lithography.

In an embodiment, the thin elastomeric substrate inner surface definesan enclosure or an interior volume having at least one opening forreceiving and covering a curved surface. In an aspect, the surface to becovered and contained within the enclosure is an object that is part ofa living animal, such as an appendage, a finger, an arm portion, a legportion, a head portion or a torso portion.

In an embodiment, the thin elastomeric substrate inner surface thatdefines the enclosure for receiving a curved surface and the substratehas physical properties to receive, accommodate and conformally contactunder a self-generated contact force, the curved surface. In an aspect,the physical properties correspond to a substrate Young's modulus thatis less than or equal to 500 kPa, and a substrate fracture strain thatis greater than or equal to 500%. Functionally, this ensures thesubstrate can conformally contact even highly irregularly shapedsurfaces and also can undergo surface flipping without adverse impact tostructural integrity.

In an aspect the enclosure has a receiving dimension that is smallerthan a corresponding dimension of the curved surface, wherein during usea strain in the thin elastomeric substrate increases the receivingdimension to accommodate the received surface within the enclosurewithout adversely impacting the functional electronic device. Forexample, if the substrate is for receiving a finger, the enclosure mayhave a diameter that is less than the diameter of the finger.Accordingly, during use the finger stretches the elastomeric substrate,thereby generating a radially-directed contact force between the fingersurface and the substrate. In this manner, the strain generates anintimate contact force between the thin elastomeric substrate and thecurved surface within the enclosure to establish and maintain intimateand conformal contact between the device component on the substrateinner surface and the curved surface.

The amount of strain in the substrate may be varied so as to control theamount of contact force between the substrate, and therefore anyfunctional devices on the inner substrate surface, and the surfacewithin the enclosure. For applications where greater contact force isrequired, a characteristic dimension of the enclosure is correspondingdecreased relative to the size of the object being accommodated. Forexample, the enclosure volume reduced by decreasing a diameter of theenclosure. In an aspect, the electronic device during use has a strainthat is selected from a range that is greater than or equal to 1% andless than or equal to 100%. Of course, due to the large fracture strainof the elastomeric substrate as well as the highly flexible and elasticelectronic devices, such as by the use of flexible and stretchableinterconnects and thin layout geometry, the invention can accommodateeven higher strains and stresses as desired.

The electronic device may be further described in terms of the enclosure(also referred herein as, and used interchangeably with, interiorportion or interior volume), including interior portion length, width,depth and/or volume. For example, the enclosure may be cylindricallyshaped with an average diameter of 5 mm to 30 cm, and/or an averagelength of 5 mm to 30 cm. In an aspect, the enclosure has a volume thatis greater than or equal to 1 cm³ and less than or equal to 10,000 cm³.

In an aspect, the electronic device is an array of electronic deviceswith an electronic device spatial density selected from a range that isbetween about 1 mm⁻² (high density coverage) and 1 cm⁻² (low densitycoverage).

In an embodiment, the enclosure has a substantially cylindrical orpartially spherical or hemispherical shape. The cylindrical shape isoptionally covered at one end, such as to cover a finger-tip.Accordingly, any of the electronic devices may have an interior portionshaped to receive a finger or a finger-tip. The cylindrical shape mayalso be a tube that is open at both ends.

In an aspect, the enclosure is a partially-closed volume, so that thecurved surface is covered such as by forcing the curved surface into theinterior portion. In contrast, an open volume refers to an enclosurehaving at least one end free to move in that is not contiguouslyconnected with another portion of the substrate. In this manner, an openvolume may correspond to wrapping the inner surface around a curvedsurface and securing a loose end of the substrate to form the interiorportion. This can be achieved by wrapping the thin elastomeric substratearound the curved surface under a longitudinally-directed tensionensures surface cover and conformal contact, under a substrateself-generated force. Alternatively, the thin elastomeric substrate canbe rolled over the biological surface under a circumferentially-directedtension, such as by forcing an opening of the partially-closed volume toopen further to receive the biological surface.

In an embodiment, any of the electronic devices described herein may bemultifunctional. Multifunctional refers to there being at least twodifferent types of functional electronic devices that provide differentfunctions, such as an electrotactile stimulator and a sensor device. Inan aspect, the inner surface supports a first array of functionalelectronic devices, and the outer surface supports a second array offunctional electronic devices, with the first array having a differentfunctionality than the second array. For example, the first array maycomprise electrotactile stimulators for interfacing with skin of aliving animal in conformal contact with the electronic devices of thefirst array, and the second array may comprise sensors for measuring aphysical parameter from tactile interaction between the electronicdevices of the second array and an external surface. Examples of sensorsinclude strain gauge sensors and tactile sensors, such aspiezoresistive, piezoelectric, capacitive and elastoresistive sensors.

In an aspect, the first array of electrotactile stimulators interfacewith skin of a living animal in accordance with a physical parametermeasured by the second array of sensors, such as sensors and stimulatorson the outside and inside of a substrate covering a finger.

In an embodiment, the array of functional electronic devices have afootprint surface area defined by the outermost members of the array.The methods of making the devices are compatible with a wide range offootprint surface areas, depending on the application of interest. Inone example, the footprint surface area is selected from a range that isgreater than or equal 0.5 cm² and less than or equal to 100 cm².

In an embodiment, the array of functional electronic devices comprise amultiplexed array of electrotactile stimulators for interfacing withliving tissue. In an aspect, the array of functional electronic devicescomprises an array of electrodes, such as electrodes for sensing anelectrical parameter and/or for application of an electrical parameter,such as electric potential. In an embodiment, each electrode comprisesan inner disk having a diameter that is less than 1 mm and an outer ringthat surrounds the inner disk, wherein the inner disk and outer ring areconcentrically positioned relative to each other, with a separationdistance between the inner disk and outer ring selected from a rangethat is greater than or equal to 100 μm and less than or equal to 500μm. In an aspect, the thickness of the electrodes is less than 1 μm,such as on the order of hundreds on nanometers (e.g., 100 nm to 900 nm).In an aspect, any of the semiconductor components comprise a siliconnanomembrane that is part of an electronic device that is a diode, suchas diode having a thickness that is less than 1 μm, or on the order ofhundreds of nanometers (e.g., 100 nm to 900 nm). The diodes andelectrodes may comprise part of a multiplexed circuit to facilitatedevice control and output processing, especially for arrays comprising alarge number of functional electronic devices.

In another embodiment, the invention is a method for making any of thedevices described herein. In an aspect, provided is a method of makingan electronic device to cover and interface with a curved surface byproviding an elastomeric substrate having an inner facing surface and anouter facing surface. A functional electronic device, such as an arrayof functional electronic devices, is transfer printed to the elastomericsubstrate outer facing surface. The elastomeric substrate is flipped, sothat after flipping the outer facing surface is the inner facing surfaceand the inner facing surface is the outer facing surface, therebyproviding the array of device components on the inner facing surface,wherein after flipping the array of functional electronic devices remainfunctional. Remain functional refers to at least 90%, at least 95%, orall functional electronic devices remaining functional after flipping.The desired functionality level is achieved by incorporating any one ormore of the device geometries provided herein, including by usingultrathin devices and device components (e.g., less than 1 μm), flexibleand stretchable interconnects, including serpentine geometries, andneutral mechanical plan (NMP) layouts. Accordingly, any one or more ofthese device layouts and geometries may be incorporated in any one ormore of the methods disclosed herein to achieve robust devices evenafter stresses associated with surface flipping.

In an aspect, the inner facing surface defines an interior volume orportion for receiving, covering and interfacing with the curved surface.In an aspect, the enclosure of the elastomeric substrate is obtained bycasting an elastomeric precursor against a curved surface or a moldthereof and curing the elastomeric precursor to obtain the elastomericsubstrate having an inner facing surface and an outer facing surface. Inthis fashion, the substrate may be tailored to specific curved surfacesthat will be used in the system. In particular, an elastomeric substratehaving a surface curvature at rest that corresponds to the curvedsurface may be generated. Optionally, the resultant cured substrate hasa slightly smaller interior volume dimension than the correspondingdimension of the object that has the to-be-received curved surface. Forexample, the mold of the surface may be correspondingly slightly reducedin size. This is one means for ensuring there is a self-generatedcontact force generated by strain of the elastomeric substrate toaccommodate the to-be-received curved surface. In an aspect, the moldsize is selected so as to generate a strain in the elastomeric substratethat is selected from a range that is greater than or equal to 1% andless than or equal to 100%, or between about 1% and 20%. Alternatively,the substrate curvature at rest may be made by another process known inthe art, such as extrusion.

In an aspect, the transfer printing comprises transferring the arrayfunctional electronic devices from a transfer stamp to an outer surfaceof the elastic substrate, such as by transfer printing (see, e.g., U.S.Pat. No. 7,943,491 (41-06); U.S. Pat. No. 7,799,699 (43-06); U.S. Pat.No. 7,932,123 (151-06); U.S. Pat. No. 8,217,381 (134-06); U.S. Pat. No.8,198,621 (38-04D), U.S. Pat. No. 7,622,367 (38-04A), all of which arespecifically incorporated by reference). In an embodiment, particularlyfor elastomeric substrates having a curved surface, the transferprinting further comprises flattening the elastomeric substrate into aflat geometry and transferring the array of functional electronic deviceto the elastic substrate in the flat geometry. After transfer, theelastomeric substrate may be released to relax back into its curvedsurface geometry. In another aspect, the transfer printing comprisesrolling the transfer stamp over the outer surface of said elasticsubstrate in a curved geometry.

In an aspect, the curved surface to-be-received in the interior volumeor portion has a surface shape that corresponds to a finger or afinger-tip surface shape.

In an aspect, the electronic device is incorporated into a finger orfingertip of a glove. In an aspect, the functional electronic devicecomprises an array of sensors, actuators, or sensors and actuators.

In an embodiment, the functional electronic device comprises an array ofelectrotactile electrodes in a mesh configuration, wherein electricalinterconnects are electrically connected to the electrotactileelectrodes.

In an aspect, the invention is a method of using any of the devicesherein, such as a method of interfacing with a surface of an object. Inan embodiment, the method comprises providing a thin elastomericsubstrate having an inner facing surface defining an enclosure, and anouter facing surface. A functional electronic device is supported on theinner facing surface or the outer facing surface. The functionalelectronic device comprises a device component that is one or moreinorganic semiconductor components, one or more metallic components, orone or more inorganic semiconductor components and one or more metalliccomponents. The functional electronic device is stretchable and bendablewith a thickness that is less than or equal to 10 μm. The surface thatsupports the functional electronic device is physically contacted withan object surface to interface the functional electronic device with theobject surface of an object. In an aspect, the enclosure receives anobject and attendant surface so as to provide physical support to thesubstrate. In an aspect, the method relates to expanding the volume ofthe enclosure so as to accommodate the object and curved surface beingreceived within the enclosure.

For devices on the inner substrate surface, the method further comprisesintroducing the surface of an object to the enclosure for interfacing.For example, the object may be part of a living animal and the objectsurface corresponds to skin or epidermal layer. The functionalelectronic device may comprise an array of sensors, actuators, or bothsensors and actuators. In an embodiment, the device comprises an arrayof electrotactile stimulators, such as for stimulating nerves in theskin or epidermal layer underlying the electrotactile stimulators.

Alternatively, for functional electronic devices supported by an outerfacing surface, the physically contacting step may comprise introducingthe surface of an object that is external to the substrate enclosure tothe outer facing surface. In this aspect, the functional electronicdevices on the outer surface interface with the externally locatedobject surface, including sensors that measure a tactile sensation. Inan aspect, the method further comprises the step of inserting asupporting object into the interior portion to physically support theelastomeric substrate. For example, in remote sensing the supportingobject may be part of a remotely controlled object or a roboticallycontrolled device. In this aspect, the functional electronic device maycomprise an array of sensors for measuring a physical parameter of theobject surface, ranging from a tactile-generated force parameter, to aninherent surface-related parameter such as temperature, conductivity,hardness, resilience or another parameter depending on the applicationof interest.

In another embodiment, a first functional electronic device is supportedby the inner facing surface and a second functional electronic device issupported by the outer facing surface, and the physically contactingstep comprises introducing a surface of a first object to the interiorportion and a surface of a second object to the outer surface. Forexample, the first object may correspond to an appendage of a livingperson, and the first functional electronic device is part of an arrayof electrotactile stimulators that interfaces with a tissue overlyingthe appendage. The appendage may be a finger or fingertip where anelectrotactile stimulation is provided that depends on the interactionof the of the second functional electronic device supported on the outersurface with the second object surface. In the case of a surgical glove,the second object surface may be part of a patient, such as biologicaltissue.

Any of the devices and processes provided herein may relate to anenclosure that receives a portion of the human body, including a finger,a fingertip or any other parts disclosed herein.

Provided herein are electronic devices configured to conform to abiological surface of user, including an epidermal layer or a skinlayer. In an embodiment, the biological surface corresponds to anappendage. In an embodiment, the biological surface is a finger ormultiple fingers, including the finger-tip. In an embodiment, thebiological surface is a part of the human body, including the epidermisor skin. The device is particularly useful for mounting to a shapedportion of a user surface, including a user surface that moves and/ordeforms. One aspect of the invention is that the electronic device isprovided on a flexible, deformable and/or bendable substrate that, whenappropriately mounted on the user, provides a self-generated force toensure the electronic device is in good contact with the user surface,with the contact well-maintained and durable even over long periods oftime, ranging from many minutes to many hours or days, as desireddepending on the application of interest.

In an embodiment, the electronic device has a substrate with athree-dimensional curvature matched to a biological surface curvature.“Three-dimensional curvature” refers to a surface that is defined by (x,y, z) co-ordinates, or transformations thereof. The curvature isconsidered “matched” to a biological surface when there is substantialcorrespondence between the substrate surface and biological surface,particularly for that portion of the substrate receiving surface thatsupports the array of components. In this embodiment, the receivingsurface of the substrate, and the array of components, is capable ofphysical contact, including conformal contact, with the biologicalsurface. The substrate receiving surface, when oriented in aninner-facing direction, defines an enclosure having an inner volume thatis configured to receive the biological surface, such as a finger,appendage, or other accessible portion of the user.

A functional benefit of the device configuration that provides anenclosure and inner volume for receiving a user body part is that thedevice substrate can provide a self-generated force to ensure intimatecontact between the biological surface and the components of the array.In an aspect, the self-generated force is sufficient that no adhesivecomponents or external force generation is required, and absence ofthose components does not impact the ability to reliably generate andmaintain conformal contact.

The self-generated force from the device substrate may be a physicalforce applied in a normal direction with respect to an individualcomponent within the array of components. Although force is applied inmultiple directions, with a direction and magnitude that may vary overthe biological surface, for an individual component a normal force onthat component can be calculated from this force distribution. Thisnormal force can be generated by various embodiments. In one embodiment,the electronic device is wrapped over a biological surface undertension, thereby providing the desired force. Alternatively, theelectronic device can be rolled over a surface, with an effectivecircumferentially-directed tension providing the normal force to ensureconformal contact between the device and the underlying biologicalsurface, even over a range of curved surfaces spatially varying overeach of the three spatial dimensions.

The configuration of the device ensures that even when the deviceexperiences substantial stresses, such as during application of thedevice to the skin, finger, or other region of the body, a majority ofthe components in the array remain functional. In an aspect, at least70%, at least 90%, at least 95%, or about all of the components orfunctional electronic devices remain functional after application to thebiological surface, including by manipulation of the surface orientationto ensure the array of components are inner-facing and positioned forphysical and/or conformal contact with the skin.

In an aspect, the device inner volume is formed by flipping the array ofcomponents supported by the receiving surface from an outer-facing to aninner-facing configuration. This aspect is particularly relevant forthose devices where the array of components is transfer printed to aphysically-accessible surface, e.g., the outer-facing surface. Such anouter-facing surface is properly configured to provide conformal contactby flipping the substrate so that the previously positionedouter-surface corresponds to the inner-facing surface.

In an embodiment, the substrate forms an open-tube volume, where thesubstrate has two open ends, and between the open ends there isconformal contact with a biological surface. Such a configuration isrelevant for devices that are slipped over an appendage with a portionof the appendage extremity not covered, such as a finger sleeve (e.g.,fingertip less gloves), arm-band, leg-band or forehead-band, or wrapsthereof. In this aspect, the inner volume does not have physical endsurfaces, but instead ends defined by the edges of the substrate.Alternatively, the substrate forms a partially closed volume, such asfor a finger confined by the fingertip portion of a glove. In thisaspect, one end of the inner volume has a corresponding physicalsurface, with the other end open to receive the biological surface. Ineither embodiment, the inner volume may be defined by a depth and adiameter, or characteristic measures thereof, including for example byaveraging over the entire substrate for those substrate shapes that arecomplicated (e.g., non-cylindrical).

The device is compatible, depending on the desired application, with anynumber or types of sensors, effectors, actuators or circuit elements,including as disclosed in any of 126-09, 29-11P, 134-06, 3-11, 7-11,150-11, 38-04C, 38-04D and any other as provided hereinbelow, which arehereby explicitly incorporated by reference for the materials,components, configurations and methods of making and using, as disclosedtherein.

In an aspect, the device is further characterized by any one or morerelevant parameters, including dimensions, array characteristicsincluding component number and density, and footprint surface area.Footprint surface area refers to the coverage area of the array, andcorresponding area of the biological surface in conformal contact withthe array of components. The device is well-suited for configurationover any size area, ranging from relatively small (e.g., 0.5 cm²) torelatively large (e.g., 100 cm² or greater).

Also provided herein are related methods for making or for using any ofthe devices disclosed herein. Various physical characteristics of thedevices provide the ability to specially manipulate the device toachieve functional benefit. For example, the substrate is capable ofbeing shaped to any desired surface and an electronically activematerial transferred thereto. For transfer printing, the outer surfaceof the substrate is configured as a receiving surface of theelectronically active material as the outer-facing surface is generallymore accessible than an inner-facing surface. The deformability of thesubstrate provides the ability to then flip the receiving surface froman outer-facing configuration to an inner-facing configuration, therebyfacilitating intimate contact between the electronically active materialwith a biological surface when the device is mounted or applied to thebiological surface.

In an aspect, the invention provides a method of making appendagemountable electronic system, the method comprising the steps of: (i)providing a flexible or stretchable substrate having an initially innerfacing surface defining an original enclosure; and an initially outerfacing surface; (ii) transfer printing a flexible or stretchableelectronic device comprising one or more sensors, actuators or both tothe initially outer facing surface of the flexible or stretchablesubstrate; the sensors, actuators or both comprising one or moreinorganic semiconductor components, one or more metallic components, orone or more inorganic semiconductor components and one or more metalliccomponents; wherein at least a portion of the inorganic semiconductorcomponents, metallic components or both has a thickness less than orequal to 500 microns; and (iii) flipping the elastomeric substrate sothat after flipping the initially outer facing surface becomes asubsequently inner facing surface defining a final enclosure forreceiving an appendage and the original inner facing surface becomes asubsequently outer facing surface, thereby providing the electronicdevice on the subsequently inner facing surface; wherein after the stepof flipping the substrate the flexible or stretchable device remainsfunctional.

In an embodiment, for example, the appendage is a hand, a finger, afinger-tip, a skull, a foot, a toe, a let, a torso, or any portionthereof. In an embodiment, for example, the step of providing theflexible or stretchable substrate comprises: (i) casting an elastomericprecursor against a surface of the appendage or a mold thereof; and (ii)curing the elastomeric precursor to obtain the flexible or stretchablesubstrate having an enclosure shape at rest that corresponds to a shapeof the appendage. In an embodiment, for example, the step of transferprinting comprises transferring an array of actuators, sensors, oractuators and sensors, via a technique selected from the groupconsisting of microtransfer printing, dry contact transfer printing,solution-based printing, soft lithography printing, replica molding, andimprint lithography. In an embodiment, for example, the step of transferprinting comprises transferring the array of actuators, sensors, oractuators and sensors from an elastomeric transfer stamp to theinitially outer surface of the elastic substrate. In an embodiment, forexample, the step of the transfer printing further comprises flatteningthe elastomeric substrate into a flat geometry and transferring thearray of actuators, sensors, or actuators and sensors to the elasticsubstrate in the flat geometry. In an embodiment, for example, the stepof the transfer printing further comprises rolling the elastomerictransfer stamp over the outer surface of the elastic substrate in acurved geometry. In an embodiment, for example, the final enclosure hasan inner surface shape that corresponds to a finger or a finger-tipsurface shape. In an embodiment, for example, the system is incorporatedinto a finger or fingertip of a glove.

In an embodiment, for example, the step of transfer printing one or moresensors, actuators or both to the subsequently outer surface of theflexible or stretchable substrate, thereby providing a first sensor, oractuator or both on the subsequently inner surface and a second sensor,or actuator or both on the subsequently outer surface. In an embodiment,for example, the first sensor, or actuator or both comprises an array ofelectrotactile stimulators, and the sensor, or actuator or bothcomprises an array of tactile sensors. In an embodiment, for example,the method further comprises the step of communicably connecting thetactile sensors with the electrotactile sensors so that theelectrotactile sensors are controlled by an output from the tactilesensors. In an embodiment, for example, the array of electrotactilesensors generate a spatially-varying pattern of electrical stimulation.

In an aspect, the substrate curvature is obtained by casting a polymeragainst a desired shape. The desired shape can be the biological surfaceitself, such as for a custom-fit application. Alternatively, the desiredshape can itself be a mold of a biological surface shape. Alternatively,substrate curvature is achieved by a non-casting process, including byuse of a commercially available substrate (e.g., a surgical glove).

An example of a method of making an appendage mountable electronicsystem by such a casting process is by: (i) providing an appendage ormold thereof; (ii) providing a flexible or stretchable electronic devicecomprising one or more sensors, actuators or both to a surface of theappendage or mold thereof; said sensors, actuators or both comprisingone or more inorganic semiconductor components, one or more metalliccomponents, or one or more inorganic semiconductor components and one ormore metallic components; wherein at least a portion of said inorganicsemiconductor components, metallic components or both has a thicknessless than or equal to 500 microns; (iii) introducing a prepolymer to theflexible or stretchable electronic device supported by the surface ofthe appendage or mold thereof; and (iv) polymerizing the prepolymer toform a flexible or stretchable substrate having an inner surface thatsupports the flexible or stretchable electronic device. Optionally, themethod further comprises the step of removing the substrate and flexibleor stretchable electronic device from the surface of the appendage ormold thereof.

Any of the methods may further comprise the step of transfer printing aflexible or stretchable electronic device comprising one or moresensors, actuators or both to an outer surface of the flexible orstretchable substrate; said sensors, actuators or both comprising one ormore inorganic semiconductor components, one or more metalliccomponents, or one or more inorganic semiconductor components and one ormore metallic components; wherein at least a portion of said inorganicsemiconductor components, metallic components or both has a thicknessless than or equal to 500 microns. In this manner, electronic devicesare provided to both internal and external surfaces without having toflip the substrate surfaces.

In an embodiment, the transfer printing comprises transferring theelectronically active material to the substrate that has been flattened.Alternatively, such as for a substrate that remains positioned againstthe user surface or mold thereof, the transfer printing can be to thecurved surface, such as by a rotational or rolling motion of the stampover the curved surface.

Without wishing to be bound by any particular theory, there may bediscussion herein of beliefs or understandings of underlying principlesrelating to the devices and methods disclosed herein. It is recognizedthat regardless of the ultimate correctness of any mechanisticexplanation or hypothesis, an embodiment of the invention cannonetheless be operative and useful.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Schematic illustration of the process for transfer printing aninterconnected device structure from a substrate on which it isfabricated to an elastomeric sheet. (a) Interconnected sensors andelectronics formed on a silicon wafer in an open mesh geometry arelifted onto the surface of a PDMS slab (i.e. stamp); (b) the backside ofthe mesh and the supporting PDMS stamp are coated with a thin layer ofSiO₂ and then pressed onto an elastomeric sheet (Ecoflex); (c) removingthe PDMS completes the transfer.

FIG. 2. Process for fabricating a multiplexed array of electrotactilestimulators in a stretchable, mesh geometry on the inner surface of anelastomeric finger-tube. (a) casting and curing an elastomer precursoron the finger of a model hand yields a thin (˜500 μm thick), closed-formmembrane, i.e. a finger-tube; (b) a PDMS stamp (here, backed by a glassmicroscope slide) delivers the electrotactile device to the outersurface of this finger-tube, while compressed into a flattened geometry;(c) electrotactile array on the outside of the freestanding finger-tube;(d) turning or flipping the tube inside out relocates the array on theinner surface of the finger-tube, shown here at the midway point of thisflipping process, so that the previous outer surface is the innersurface and the previous inner surface is the outer surface.

FIG. 3. Mechanics modeling of the “flipping-over” process andapplication to arrays of electrotactile stimulators multiplexed with SiNM diodes. (a) Calculated (analytical and FEM) profiles of an Ecoflexfinger-tube during bending associated with flipping the tube inside out,showing a linear relationship between the radius (R_(radial)=7.5 mm) ofthe tube and the minimum bending radius (R_(axial)); (b) FEM results formaximum strains on the inner and outer surfaces during this process; (c)schematic illustration of a multiplexed electrotactile array withserpentine mesh interconnects, with magnified diagram (right top) andimage (right bottom) of a PIN Si NM diode (after flipping-over); (d)schematic cross sectional illustrations of two regions of the device,with the position of the NMP indicated with a dashed red line, andanalytical results for the maximum strains during the flipping-overprocess; (e) I-V characteristics of a Si NM diode before and afterflipping-over; (f) maximum strain in the Si NM diode and h_(NMP) (theoffset between the neutral mechanical plane and the lower surface of theSi NM) as a function of thickness of the Si NM.

FIG. 4. Mechanics and electrical characteristics of a 2×3, multiplexedelectrotactile array on a fingertube. (a) Voltage required forelectrotactile sensation as a function of stimulation frequency. Inset:electrotactile array on human finger during experiments; (b) I-Vcharacteristics of multiplexed electrotactile electrodes in contact witha human thumb; (c) circuit diagram of the diode multiplexing scheme; (d)function table showing inputs for addressing each of the six channels(H=High; L=Low).

FIG. 5. Detection of finger motion with arrays of stretchable Si NMstrain gauges. (a) FEM results of the maximum principle strain for a 1×4array of gauges (straight, vertical structures near the top of theserpentine interconnect mesh) due to an overall 10% strain applied alongthe longitudinal (y) direction. The upper inset shows the strains in thegauge highlighted by the yellow dashed box. The lower inset provides animage of a fabricated device with a layout that matches that of the FEMresults; (b) experimentally measured and analytically calculated changesin resistance for a representative Si NM strain gauge as a function ofapplied strain along the longitudinal direction. The inset provides anSEM image of a portion of the device, with the Si NM gauge located inthe dashed box; (c) images of a strain gauge array on a finger-tubemounted on the thumb, in straight (I) and bent (II) positions; (d)change in resistance of a representative gauge during three bendingcycles (black) and side-to-side motion (red); (e) images of a straingauge array on a thin, elastomeric sheet laminated onto the metacarpalregion of the thumb in straight (III) and sideways deflected (IV)positions; (f) change in resistance of gauges at two ends of the arrayduring three cycles of side-to-side motion.

FIG. 6. Tactile sensing with integrated capacitance sensors. (a) sensorson the anterior of the thumb; (b) inner electrodes for a 2×3 array ofsensors (electrotactile electrodes); (c) outer electrodes for the samearray; (d) measured and analytically calculated change in capacitance ofa single sensor with applied pressure and tensile strain.

FIG. 7. Schematic of the basic fabrication process. (a) Si substrate;(b) spin coat sacrificial PMMA; (c) spin coat polyimide (PI)precursor/250° C. bake in inert atmosphere; (d) Auevaporation/patterning; (e) spin coat PI precursor/250° C. bake in inertatmosphere; (f) O₂ RIE to expose Au electrodes and form PI meshstructure; (g) PMMA undercut in acetone/application of PDMS stamp; (h)devices transferred to PDMS stamp; (i) Cr/SiO₂ evaporated onto back ofdevice; (j) PDMS stamp pressed onto UV exposed Ecoflex; (k) transfercompleted with PDMS stamp removal.

FIG. 8. Schematic illustration of the flipped-over elastomeric Ecoflextube in the plastic hand model.

FIG. 9. Schematic illustration of an array of functional electronicdevices on an inner surface of an elastomeric substrate.

FIG. 10. Schematic of silicon transfer printing. (a) silicon oninsulator (SOI) substrate; (b) RIE etch release holes (3 μm) in Silayer; (c) wet etch (buffered oxide etch) of SiO2 layer to release Silayer; (d) PDMS stamp pressed into contact with Si; (e) Si transfer toPDMS stamp upon removal; (f) PDMS stamp with transferred Si pressed ontoPI layer; (g) After heating at 150° C. for 4 min, Si transferred todevice upon stamp removal.

FIG. 11. Schematic of the fabrication process for electrotactilestimulators. (a) silicon substrate; (b) spin coat 100 nm sacrificialPMMA; (c) spin coat/250° C. bake 1.2 μm polyimide; (d) transfer of Silayer with PIN diodes (release holes not shown); (e) RIE isolation of Sinanomembrane PIN diodes and Au evaporation/patterning; (f) spincoat/250° C. bake 1.2 μm polyimide; (g) contact vias for diodes formedin PI with O2 RIE; (h) Au evaporation/patterning; (i) spin coat/250° C.bake 1.2 μm polyimide; (j) O2 RIE to form polyimide mesh structure andexpose electrotactile electrodes.

FIG. 12. Schematic of the fabrication process for strain gauges. (a)silicon substrate; (b) spin coat 100 nm sacrificial PMMA; (c) spincoat/250° C. bake 1.2 μm polyimide; (d) transfer of p-doped Si (releaseholes not shown); (e) RIE isolation of Si strain gauge nanomembranes;(f) Au evaporation/patterning; (g) spin coat/250° C. bake 1.2 μmpolyimide; (h) O2 RIE to form polyimide mesh structure.

FIG. 13. Schematic of the fabrication process for tactile electrodes.(a) silicon substrate; (b) spin coat 100 nm sacrificial PMMA; (c) spincoat/250° C. bake 1.2 μm polyimide; (d) Au evaporation/patterning; (e)spin coat/250° C. bake 1.2 μm polyimide; (f) O2 RIE to form polyimidemesh structure.

FIG. 14(A-C) provides different views of an appendage mountableelectronic system of the invention.

FIG. 15 provides view of an appendage mountable electronic system of theinvention accommodating an appendage and interacting with an externalsurface.

FIG. 16 shows a system having electronic devices supported on the innersurface 30 of the substrate.

FIG. 17 shows a method for making an appendage mountable electronicsystem of the invention.

FIG. 18 is a process flow summary of one embodiment for making any ofthe systems disclosed herein.

FIG. 19 is a schematic of a capacitance-based tactile sensor on bothinner and outer substrate surfaces.

FIG. 20 is a process flow summary of one embodiment for making any ofthe systems disclosed herein by casting a substrate against an objectsurface.

DETAILED DESCRIPTION OF THE INVENTION

In general, the terms and phrases used herein have their art-recognizedmeaning, which can be found by reference to standard texts, journalreferences and contexts known to those skilled in the art. The followingdefinitions are provided to clarify their specific use in the context ofthe invention.

“Enclosure”, “interior volume”, or “interior portion” are usedinterchangeably and refers to the space bounded by the inner surface ofthe elastomeric substrate. Accordingly, in aspects where the innersurface defines a small enclosure, or having an access opening that issmall, the enclosure interior volume is correspondingly confined and notreadily accessible from the outside. This confinement may make it notpractical to reliably place and position functional electronic deviceson the inner surface defining the enclosure. The invention is compatiblewith a wide range of substrates. For example, the substrate may bedescribed in terms of various physical properties, such as a modulus ora thickness. In an embodiment, the modulus is a Young's modulus that isless than about 50 MPa, such as between about 100 kPa and 50 MPa. In anembodiment, the thickness is less than 1 mm, such as between about 0.1mm and 1 mm.

As used herein, “conform” refers to a substrate which has a bendingstiffness that is sufficiently low to allow the device, material orsubstrate to adopt any desired contour profile, for example a contourprofile allowing for conformal contact with a surface having athree-dimensional curvature, including a curvature that may change overtime or during use. The surface curvature may be highly irregular, inthat the surface to be covered may have major surfaces that face eachother. Accordingly, the conform aspect is not simply an overlay of asubstantially two dimensional surface, but rather relates to covering asurface of a three-dimensional object having a defined volume.

“Appendage” is used broadly herein to refer to any three-dimensionalobject with a three-dimensional volume defined by one or more curvedand/or planar surfaces. In certain embodiments, the appendagecorresponds to living tissue. In an aspect, the appendage is a livingtissue in a biological environment, such as part of a living animal. Inan embodiment, the appendage surface corresponds to bone, skin or anepidermal layer of a living animal, including a human, so that the innersurface of the flexible or stretchable substrate conforms to one or moresurface(s) of living tissue. Examples of appendages from a living animalinclude, but are not limited to, a hand, a finger, a finger-tip, a bone,a skull, a tooth, a head, a foot, a toe, a leg, an arm, a torso, a nose,an ear, genitalia or any portions thereof. In certain embodiments, theappendage corresponds to a non-living object, such as objects ofremotely controlled instruments, robotics and the like, including forremote sensing applications. “Conformable” refers to a device, materialor substrate which has a bending stiffness that is sufficiently low toallow the device, material and/or substrate to adopt any desired curvedsurface, for example for conformal contact with a surface having highcurvatures. In certain embodiments, the curved surface is an appendageof a user.

“Conformal contact” refers to contact established between a device and areceiving surface. In one aspect, conformal contact involves amacroscopic adaptation of one or more surfaces (e.g., contact surfaces)of a device to the overall shape of a surface. In another aspect,conformal contact involves a microscopic adaptation of one or moresurfaces (e.g., contact surfaces) of a device to a surface resulting inan intimate contact substantially free of voids. In an embodiment,conformal contact involves adaptation of a contact surface(s) of thedevice to a receiving surface(s) such that intimate contact is achieved,for example, wherein less than 20% of the surface area of a contactsurface of the device does not physically contact the receiving surface,or optionally less than 10% of a contact surface of the device does notphysically contact the receiving surface, or optionally less than 5% ofa contact surface of the device does not physically contact thereceiving surface. In an embodiment, a method of the invention comprisesestablishing conformal contact between an inner surface of theelastomeric substrate that defines an enclosure and an object beinginserted into the enclosure. Optionally, the conformal contact furtherincludes one or more single crystalline inorganic semiconductorstructures, one or more dielectric structures and/or one or moremetallic conductor structures supported by the elastomeric substrateinner surface and a curved surface within the enclosure.

“Cover”, as used herein refers to the conformal contact region betweenthe elastomeric substrate inner surface and an object surface that iswithin the enclosure defined by the elastomeric substrate inner surface,specifically under a self-generated contact force that prevents relativemovement between the two surfaces. In an aspect, the substrate portionsthat cover may have a constant and uniform thickness. In an aspect, thecover may have a spatial distribution of substrate thicknesses.Alternatively, cover includes embodiments where the substrate hasperforations, such as a mesh or woven configuration, so as to permitsurface breathability. The contact force may be uniformly distributedacross the cover area or, alternatively, may be spatially distributedsuch as certain locations where it is critical the surfaces do not movewith respect to each other having a higher contact force. That positioncould correspond, for example, to positions having a high functionalelectronic device density.

“Open mesh geometry” refers to a material having at least 20%, at least40%, at least 60%, or at between about 20% and 80% of the surface areaof the material that is open or void space, as defined by an outerperimeter of the material. Accordingly, the material may refer toelectrical interconnects that overlay a substrate that may be acontinuous surface or may itself be mesh. Interconnects having such anopen mesh geometry are optionally tethered to a substrate surface eitherdirectly, or indirectly such as at ends connected to rigid deviceislands that are bonded to the substrate. Such mesh geometry may have anoticeable longitudinally-defined axis, including multiple axis havingdifferent alignments to facilitate bending and stretching in more thanone direction. In an aspect, the mesh has two directions that areorthogonal or substantially orthogonal with respect to each other. In anaspect, substantially orthogonal refers to within about 10° of absoluteperpendicular.

“Closed tube geometry” refers to a substrate having ends that areconstrained and unable to move without substantially affecting otherportions of the substrate. One example of a closed tube geometry is endsof a rectangular substrate that are joined into a cylindrical tube, forexample.

Any of the flexible or stretchable substrates can be further defined interms of “lateral dimensions”, such as lateral dimensions for receivingan appendage surface. Examples of lateral dimensions include a length,diameter or perimeter along selected cross-sections. The substrate mayalso be defined in terms of a surface area, such as a surface areaavailable for conformal contact to a surface of the appendage or forcontact with an external surface. One advantage of the systems andmethods provided herein is that they are compatible with a wide range ofdimensions and are selected depending on the application of interest,ranging from 1 mm to 10 cm for small scale, up to and including 10 cm to1000 cm scale for larger scale applications.

A central aspect of the various embodiments is an elastomeric substratethat provides a self-generated force to provide and maintain intimateand conformal contact with an object surface in the enclosure.Accordingly, one aspect of any of the devices and methods providedherein is an enclosure having an expandable and adjustable interiorvolume (in terms of both magnitude and shape) so as to accommodate orreceive objects that are bigger than the at-rest enclosure volume orsize. For example, a substrate that stretches or is actively stretchedto accommodate a curved surface within the enclosure or interiorportion, so that the inner surface is in conformal contact with thesurface. This can be achieved such as by a substrate interior volumethat is sized smaller than the to-be-received surface for an interiorvolume that is a closed surface. Alternatively, such as for an interiorvolume that is open, the substrate may be wrapped around the surfaceunder tension, thereby ensuring intimate and conformal contact betweenan inner surface and the accommodated surface. The ends of the substratemay be fixed in position by an adhesive, a bonding mechanism (e.g.,snaps, Velcro, hooks, and the like), or via self-adhesion. This aspectof a self-generated contact force to provide and maintain conformalcontact, is particularly useful under strenuous operating conditionsthat would otherwise adversely affect conformal contact and, therefore,device fidelity. For example, a relatively high contact force may beemployed in conditions involving vigorous and substantial movement andforces.

“Interchangeably flippable” refers to a substrate that can be turnedinside-out without permanently impacting a substrate mechanical propertyor adversely affecting a functionality parameter of the functionalelectronic device.

“Functionality parameter” is used to assess whether an electronic deviceremains functional and/or the degree of functionality or damage. Forexample, many of the devices and methods provided herein relate toflipping of surfaces to which functional electronic devices aresupported. Such flipping is associated with relatively high localizedstresses, strains and bending moments. One important functional benefitof the instant invention is the ability to perform such flipping withoutadversely impacting the associated devices or device components.Conventional electronic devices that are not bendable and flexiblyeither break outright or have their functionality severely impacted bythe act of surface flipping. One manner of quantifying this functionalbenefit is by comparing device performance before and after theflipping, referred broadly herein as a “functionality parameter”. In anaspect, functionality parameter can reflect whether a functionalelectronic device is operating by assessing the output based on an inputthat is a physical signal (for a sensor) or an electronic input (for anactuator). This indication is appropriate for assessing degree ofnon-functionality by deviation for the equivalent input prior toflipping, or total non-functionality. In this case, a user-selectedtolerance is selected, such as outputs that within 20%, within 10%, orwithin 5%, reflected as satisfying functionality. “Without substantialdegradation” of a functionality parameter refers to a device satisfyingthe 20%, 10%, or 5% tolerance when referring to an individual functionalelectronic device. In an array aspect, it refers to at least 80%, atleast 90%, or at least 95% of the array devices remaining functionalafter flipping.

“Functional electronic device” refers to an electronic device, such as asensor or actuator, which interfaces with a surface that is brought intocontact with the device. A functional electronic device provides usefulinformation about the interfacing. For example, for tactile sensors thedevice provides an output that is proportional to a force between thesensor and the surface. For an electrotactile stimulator, there is anelectric stimulation or actuation of a nerve underlying the stimulator.A positioning sensor, in contrast, provides an output that is based onthe movement of the sensor and so does not interface with a surface, perse, but is still included within the scope of functional electronicdevice. Accordingly, “functional electronic device” is used broadlyherein and includes any sensors or actuators having suitably thingeometry and layouts to maintain or facilitate high degree offlexibility and stretchability. Examples of functional electronicdevices include: electrodes, actuators, strain sensors, motion sensors,displacement sensors, acceleration sensors, pressure sensors, forcesensors, chemical sensors, pH sensors, tactile sensors, optical sensors,electromagnetic radiation sources, temperature sensors, heat sources,capacitive sensors; and combinations thereof. Tactile sensors provide anoutput that is proportional to a force between the sensor and thesurface. An electrotactile stimulator provides an electric stimulationor actuation of a nerve underlying the stimulator, so as to provide atype of virtual reality system.

A “device component” is used broadly to refer to an individual part of adevice but that, in and of itself, is insufficient to provide functionalinformation. An “interconnect” is one example of a component, and refersto an electrically conducting structure capable of establishing anelectrical connection with another component or between components. Inparticular, an interconnect may establish electrical contact betweencomponents that are separate. Depending on the desired devicespecifications, operation, and application, an interconnect is made froma suitable material. Suitable conductive materials includesemiconductors and metallic conductors. Another useful device componentis a thin nanomembrane, which may form part of a diode. Accordingly, afunctional electronic device may be characterized as made up of a devicecomponent.

Other components include, but are not limited to, thin film transistors(TFTs), transistors, diodes, electrodes, integrated circuits, circuitelements, control elements, photovoltaic elements, photovoltaic elements(e.g. solar cell), sensors, light emitting elements, actuators,piezoelectric elements, receivers, transmitters, microprocessors,transducers, islands, bridges and combinations thereof. Components maybe connected to one or more contact pads as known in the art, such as bymetal evaporation, wire bonding, and application of solids or conductivepastes, for example, thereby forming device islands. Electronic devicesof the invention may comprise one or more components, optionallyprovided in an interconnected configuration.

“Electronic device” generally refers to a device incorporating aplurality of components and functional electronic devices, and includeslarge area electronics, printed wire boards, integrated circuits,arrays, biological and/or chemical sensors, physical sensors (e.g.,temperature, strain, etc.), nanoelectromechanical systems,microelectromechanical systems, photovoltaic devices, communicationsystems, medical devices, optical devices and electro-optic devices. Anelectronic device may sense a property of the surface and/or may controla property of the surface.

“Sensing” and “sensor” refers to a functional electronic device ordevice component useful for detecting the presence, absence, amount,magnitude or intensity of a physical, biological state, and/or chemicalproperty. Useful electronic device components for sensing include, butare not limited to electrode elements, chemical or biological sensorelements, pH sensors, temperature sensors, tactile sensors, strainsensors, mechanical sensors, position sensors, optical sensors andcapacitive sensors. Useful functional electronic devices include variousdevice components operably arranged to provide electrodes for detectingadjacent electric potential, sensors for detecting a biologicalcondition (e.g., disease state, cell type, cell condition) or achemical, pH, temperature, pressure, position, electromagnetic radiation(including over desired wavelengths such as associated with afluorescent dye injected into tissue), electric potential.

“Actuating” and “actuator” refers to a functional electronic device ordevice component useful for interacting with, stimulating, controlling,or otherwise affecting an external structure, material or fluid, forexample a target tissue that is biological tissue. Useful actuatingelements include, but are not limited to, electrode elements,electromagnetic radiation emitting elements, light emitting diodes,lasers and heating elements. Functional electronic devices includeactuators that are electrodes for providing a voltage or current to atissue, sources of electromagnetic radiation for providingelectromagnetic radiation to a tissue, such LEDs. Actuators also includeablation sources for ablating tissue, thermal sources for heatingtissue, displacement sources for displacing or otherwise moving atissue, reservoirs of biologics or chemicals for releasing biologics orchemicals to affect biological function, such as a biological responseincluding cell death, cell proliferation, or cell therapy by applicationof biologics or chemicals. An actuator may be an electrotactile sensor.

A “tactile sensor” refers to a transducer that is sensitive to touch,such as by transducing force or pressure into a voltage output from thesensor. An “electrotactile stimulator” refers to an electronic devicethat electrically stimulates nerves of the skin to simulate a sensation,and may be classified as an actuator.

“Semiconductor” refers to any material that is an insulator at a verylow temperature, but which has an appreciable electrical conductivity ata temperature of about 300 Kelvin. In the present description, use ofthe term semiconductor is intended to be consistent with use of thisterm in the art of microelectronics and electronic devices. Usefulsemiconductors include those comprising elemental semiconductors, suchas silicon, germanium and diamond, and compound semiconductors, such asgroup IV compound semiconductors such as SiC and SiGe, group III-Vsemiconductors such as AlSb, AlAs, AlN, AlP, BN, BP, BAs, GaSb, GaAs,GaN, GaP, InSb, InAs, InN, and InP, group III-V ternary semiconductorsalloys such as Al_(x)Ga_(1-x)As, group II-VI semiconductors such asCsSe, CdS, CdTe, ZnO, ZnSe, ZnS, and ZnTe, group I-VII semiconductorssuch as CuCl, group IV-VI semiconductors such as PbS, PbTe, and SnS,layer semiconductors such as Pbl₂, MoS₂, and GaSe, oxide semiconductorssuch as CuO and Cu₂O. The term semiconductor includes intrinsicsemiconductors and extrinsic semiconductors that are doped with one ormore selected materials, including semiconductors having p-type dopingmaterials and n-type doping materials, to provide beneficial electronicproperties useful for a given application or device. The termsemiconductor includes composite materials comprising a mixture ofsemiconductors and/or dopants. Specific semiconductor materials usefulfor some embodiments include, but are not limited to, Si, Ge, Se,diamond, fullerenes, SiC, SiGe, SiO, SiO₂, SiN, AlSb, AlAs, AlIn, AlN,AlP, AlS, BN, BP, BAs, As₂S₃, GaSb, GaAs, GaN, GaP, GaSe, InSb, InAs,InN, InP, CsSe, CdS, CdSe, CdTe, Cd₃P₂, Cd₃As₂, Cd₃Sb₂, ZnO, ZnSe, ZnS,ZnTe, Zn₃P₂, Zn₃As₂, Zn₃Sb₂, ZnSiP₂, CuCl, PbS, PbSe, PbTe, FeO, FeS₂,NiO, EuO, EuS, PtSi, TlBr, CrBr₃, SnS, SnTe, Pbl₂, MoS₂, GaSe, CuO,Cu₂O, HgS, HgSe, HgTe, HgI₂, MgS, MgSe, MgTe, CaS, CaSe, SrS, SrTe, BaS,BaSe, BaTe, SnO₂, TiO, TiO₂, Bi₂S₃, Bi₂O₃, Bi₂Te₃, BiI₃, UO₂, UO₃,AgGaS₂, PbMnTe, BaTiO₃, SrTiO₃, LiNbO₃, La₂CuO₄, La_(0.7)Ca_(0.3)MnO₃,CdZnTe, CdMnTe, CuInSe₂, copper indium gallium selenide (CIGS), HgCdTe,HgZnTe, HgZnSe, PbSnTe, TI₂SnTe₅, TI₂GeTe₅, AlGaAs, AlGaN, AlGaP,AlInAs, AlInSb, AlInP, AlInAsP, AlGaAsN, GaAsP, GaAsN, GaMnAs, GaAsSbN,GaInAs, GaInP, AlGaAsSb, AlGaAsP, AlGaInP, GaInAsP, InGaAs, InGaP,InGaN, InAsSb, InGaSb, InMnAs, InGaAsP, InGaAsN, InAlAsN, GaInNAsSb,GaInAsSbP, and any combination of these. Porous silicon semiconductormaterials are useful for aspects described herein. Impurities ofsemiconductor materials are atoms, elements, ions and/or molecules otherthan the semiconductor material(s) themselves or any dopants provided tothe semiconductor material. Impurities are undesirable materials presentin semiconductor materials which may negatively impact the electronicproperties of semiconductor materials, and include but are not limitedto oxygen, carbon, and metals including heavy metals. Heavy metalimpurities include, but are not limited to, the group of elementsbetween copper and lead on the periodic table, calcium, sodium, and allions, compounds and/or complexes thereof.

A “semiconductor component” broadly refers to any semiconductormaterial, composition or structure, and expressly includes high qualitysingle crystalline and polycrystalline semiconductors, semiconductormaterials fabricated via high temperature processing, dopedsemiconductor materials, inorganic semiconductors, and compositesemiconductor materials.

“Nanostructured material” and “microstructured material” refer tomaterials having one or more nanometer-sized and micrometer-sized,respectively, physical dimensions (e.g., thickness) or features such asrecessed or relief features, such as one or more nanometer-sized andmicrometer-sized channels, voids, pores, pillars, etc. The relieffeatures or recessed features of a nanostructured material have at leastone physical dimension selected from the range of 1-1000 nm, while therelief features or recessed features of a microstructured material haveat least one physical dimension selected from the range of 1-1000 μm.Nanostructured and microstructured materials include, for example, thinfilms (e.g., microfilms and nanofilms), porous materials, patterns ofrecessed features, patterns of relief features, materials havingabrasive or rough surfaces, and the like. A nanofilm structure is alsoan example of a nanostructured material and a microfilm structure is anexample of a microstructured material. In an embodiment, the inventionprovides device comprising one or more nanostructured or microstructuredinorganic semiconductor components, one or more nanostructured ormicrostructured metallic conductor components, one or morenanostructured or microstructured dielectric components, one or morenanostructured or microstructured encapsulating layers and/or one ormore nanostructured or microstructured substrate layers.

A component may be a nanomembrane material. A “nanomembrane” is astructure having a thickness selected from the range of 1-1000 nm oralternatively for some applications a thickness selected from the rangeof 1-100 nm, for example provided in the form of a ribbon, cylinder orplatelet. In some embodiments, a nanoribbon is a semiconductor,dielectric or metallic conductor structure of an electronic device. Insome embodiments, a nanoribbon has a thickness less than 1000 nm andoptionally less than 100 nm. In some embodiments, a nanoribbon has ratioof thickness to a lateral dimension (e.g., length or width) selectedfrom the range of 0.1 to 0.0001.

“Neutral mechanical plane” (NMP) refers to an imaginary plane existingin the lateral, b, and longitudinal, l, directions of a device. The NMPis less susceptible to bending stress than other planes of the devicethat lie at more extreme positions along the vertical, h, axis of thedevice and/or within more bendable layers of the device. Thus, theposition of the NMP is determined by both the thickness of the deviceand the materials forming the layer(s) of the device. In an embodiment,a device of the invention includes one or more inorganic semiconductorcomponents, one or more metallic conductor components or one or moreinorganic semiconductor components and one or more metallic conductorcomponents provided coincident with, or proximate to, the neutralmechanical plane of the device. Examples of a variety of NMP systemsincorporating multiple layers are provided, for example, in U.S. Pat.Pub. No. 2010/0002402, which is specifically incorporated by referencefor methods of positioning NMP.

“Coincident” refers to the relative position of two or more objects,planes or surfaces, for example a surface such as a neutral mechanicalplane that is positioned within or is adjacent to a layer, such as afunctional layer, substrate layer, or other layer. In an embodiment, aneutral mechanical plane is positioned to correspond to the moststrain-sensitive layer or material within the layer.

“Proximate” refers to the relative position of two or more objects,planes or surfaces, for example a neutral mechanical plane that closelyfollows the position of a layer, such as a functional layer, substratelayer, or other layer while still providing desired conformabilitywithout an adverse impact on the strain-sensitive material physicalproperties. “Strain-sensitive” refers to a material that fractures or isotherwise impaired in response to a relatively low level of strain. Ingeneral, a layer having a high strain sensitivity, and consequentlybeing prone to being the first layer to fracture, is located in thefunctional layer, such as a functional layer containing a relativelybrittle semiconductor or other strain-sensitive device element. Aneutral mechanical plane that is proximate to a layer need not beconstrained within that layer, but may be positioned proximate orsufficiently near to provide a functional benefit of reducing the strainon the strain-sensitive device element when the device is conformed to atissue surface. In some embodiments, proximate to refers to a positionof a first element within 100 microns of a second element, or optionallywithin 10 microns for some embodiments, or optionally within 1 micronsfor some embodiments.

A “component” is used broadly to refer to a material or individualcomponent used in a device. An “interconnect” is one example of acomponent and refers to an electrically conducting material capable ofestablishing an electrical connection with a component or betweencomponents. In particular, an interconnect may establish electricalcontact between components that are separate and/or can move withrespect to each other. Depending on the desired device specifications,operation, and application, an interconnect is made from a suitablematerial. For applications where a high conductivity is required,typical interconnect metals may be used, including but not limited tocopper, silver, gold, aluminum and the like, and alloys. Suitableconductive materials further include semiconductors, such as silicon andGaAs and other conducting materials such as indium tin oxide.

An interconnect that is “stretchable” or “flexible” is used herein tobroadly refer to an interconnect capable of undergoing a variety offorces and strains such as stretching, bending and/or compression in oneor more directions without adversely impacting electrical connection to,or electrical conduction from, a device component. Accordingly, astretchable interconnect may be formed of a relatively brittle material,such as GaAs, yet remain capable of continued function even when exposedto a significant deformatory force (e.g., stretching, bending,compression) due to the interconnect's geometrical configuration. In anexemplary embodiment, a stretchable interconnect may undergo strainlarger than 1%, optionally 10% or optionally 30% or optionally up to100% without fracturing. In an example, the strain is generated bystretching an underlying elastomeric substrate to which at least aportion of the interconnect is bonded. For certain embodiments, flexibleor stretchable interconnects include interconnects having wavy,meandering or serpentine shapes.

In the context of this description, a “bent configuration” refers to astructure having a curved conformation resulting from the application ofa force. Bent structures may have one or more folded regions, convexregions, concave regions, and any combinations thereof. Useful bentstructures, for example, may be provided in a coiled conformation, awrinkled conformation, a buckled conformation and/or a wavy (i.e.,wave-shaped) configuration. Bent structures, such as stretchable bentinterconnects, may be bonded to a flexible substrate, such as a polymerand/or elastic substrate, in a conformation wherein the bent structureis under strain. In some embodiments, the bent structure, such as a bentribbon structure, is under a strain equal to or less than 30%,optionally a strain equal to or less than 10%, optionally a strain equalto or less than 5% and optionally a strain equal to or less than 1% inembodiments preferred for some applications. In some embodiments, thebent structure, such as a bent ribbon structure, is under a strainselected from the range of 0.5% to 30%, optionally a strain selectedfrom the range of 0.5% to 10%, and optionally a strain selected from therange of 0.5% to 5%. Alternatively, the stretchable bent interconnectsmay be bonded to a substrate that is a substrate of a device component,including a substrate that is itself not flexible. The substrate itselfmay be planar, substantially planar, curved, have sharp edges, or anycombination thereof. Stretchable bent interconnects are available fortransferring to any one or more of these complex substrate surfaceshapes.

A “device component” is used to broadly refer to an individual componentwithin an electrical, optical, mechanical or thermal device. Componentsinclude, but are not limited to, a photodiode, LED, TFT, electrode,semiconductor, other light-collecting/detecting components, transistor,integrated circuit, contact pad capable of receiving a device component,thin film devices, circuit elements, control elements, microprocessors,transducers and combinations thereof. A device component can beconnected to one or more contact pads as known in the art, such as metalevaporation, wire bonding, application of solids or conductive pastes,for example. Electrical device generally refers to a deviceincorporating a plurality of device components, and includes large areaelectronics, printed wire boards, integrated circuits, device componentsarrays, biological and/or chemical sensors, physical sensors (e.g.,temperature, light, radiation, etc.), solar cell or photovoltaic arrays,display arrays, optical collectors, systems and displays.

“Island” or “device island” refers to a relatively rigid device elementor component of an electronic device comprising multiple semiconductorelements or active semiconductor structures. “Bridge” or “bridgestructure” refers to stretchable or flexible structures interconnectingtwo or more device islands or one device island to another devicecomponent. Specific bridge structures include flexible semiconductorinterconnects.

“Encapsulate” refers to the orientation of one structure such that it isat least partially, and in some cases completely, surrounded by one ormore other structures, such as a substrate, adhesive layer orencapsulating layer. “Partially encapsulated” refers to the orientationof one structure such that it is partially surrounded by one or moreother structures, for example, wherein 30%, or optionally 50% oroptionally 90%, of the external surfaces of the structure is surroundedby one or more structures. “Completely encapsulated” refers to theorientation of one structure such that it is completely surrounded byone or more other structures. The invention includes devices havingpartially or completely encapsulated inorganic semiconductor components,metallic conductor components and/or dielectric components, for example,via incorporation a polymer encapsulant, such as an elastomerencapsulant.

“Barrier layer” refers to a device component spatially separating two ormore other device components or spatially separating a device componentfrom a structure, material or fluid external to the device. In oneembodiment, a barrier layer encapsulates one or more device components.In embodiments, a barrier layer separates one or more device componentsfrom an aqueous solution, a biological tissue and/or a biologicalenvironment. In some embodiments, a barrier layer is a passive devicecomponent. In some embodiments, a barrier layer is a functional, butnon-active, device component. In a specific embodiment, a barrier layeris a moisture barrier. As used herein, the term “moisture barrier”refers to a barrier layer which provides protection to other devicecomponents from bodily fluids, ionic solutions, water or other solvents.In one embodiment, a barrier layer provides protection to an externalstructure, material or fluid, for example, by preventing leakage currentfrom escaping an encapsulated device component and reaching the externalstructure, material or fluid. In a specific embodiment, a barrier layeris a thermal barrier. As used herein, the term “thermal barrier” refersto a barrier layer which acts as a thermal insulator, preventing,reducing or otherwise limiting the transfer of heat from one devicecomponent to another or from a device component to an externalstructure, fluid or material. Useful thermal barriers include thosecomprising materials having a thermal conductivity of 0.3 W/m·K or less,such as selected over the range of 0.001 to 0.3 W/m·K. In someembodiments, a thermal barrier comprises active cooling components, suchas components known in the art of thermal management, such asthermoelectric cooling devices and systems. Thermal barriers alsoinclude those barriers comprising thermal management structures, such asstructures useful for transporting heat away from a portion of a deviceor tissue; in these and other embodiments, a thermal barrier comprisesthermally conductive material, for example material having a highthermal conductivity, such as a thermal conductivity characteristic of ametal.

“Biocompatible” refers to a material that does not elicit animmunological rejection or detrimental effect, referred herein as anadverse immune response, when it is disposed within an in-vivobiological environment. For example, a biological marker indicative ofan immune response changes less than 10%, or less than 20%, or less than25%, or less than 40%, or less than 50% from a baseline value when abiocompatible material is implanted into a human or animal.Alternatively, immune response may be determined histologically, whereinlocalized immune response is assessed by visually assessing markers,including immune cells or markers that are involved in the immuneresponse pathway, in and adjacent to the implanted device. In an aspect,a biocompatible device does not observably change immune response asdetermined histologically. In some embodiments, the invention providesbiocompatible devices configured for long-term implantation, such as onthe order of weeks to months, without invoking an adverse immuneresponse. The implantation does contemplate some immune response andassociated scarring as may occur for any minimally invasive procedures,so long as the immune response is locally confined, transient and doesnot lead to large-scale inflammation and attendant deleterious effectsand the implanted device does not substantially elevate the responsecompared to the corresponding physical trauma only.

“Bioinert” refers to a material that does not elicit an immune responsefrom a human or animal when it is disposed within an in-vivo biologicalenvironment. For example, a biological marker indicative of an immuneresponse remains substantially constant (plus or minus 5% of a baselinevalue) when a bioinert material is implanted into a human or animal. Insome embodiments, the invention provides bioinert systems, devices andrelated methods.

“Multiplexed” refers to an electronic circuit to provide convenientcontrol over an array of elements. For example, PCT Pub. WO2011/084450(126-09WO) describes multiplexing circuits in electrophysiologyapplications, which is specifically incorporated by reference. Otherexamples include, U.S. Patent Application Publication 2003/0149456discloses a multi-electrode cardiac lead adapter which incorporates amultiplexing circuit allowing for control by a conventional single leadcardiac pacing pulse generator. Similarly, U.S. Patent ApplicationPublication 2006/0173364 discloses a multichannel electrophysiologyacquisition system which utilizes a digital multiplexing circuit buildon a conventional integrated circuit.

“Ultrathin” refers to devices of thin geometries that exhibit extremelevels of bendability. In an embodiment, ultrathin refers to circuitshaving a thickness less than 1 μm, less than 600 nm or less than 500 nm.In an embodiment, a multilayer device that is ultrathin has a thicknessless than 200 μm, less than 50 μm, or less than 10 μm.

“Thin layer” refers to a material that at least partially covers anunderlying substrate, wherein the thickness is less than or equal to 300μm, less than or equal to 200 μm, or less than or equal to 50 μm.Alternatively, the layer is described in terms of a functionalparameter, such as a thickness that is sufficient to isolate orsubstantially reduce the strain on the electronic device, and moreparticularly a functional layer in the electronic device that issensitive to strain.

“Polymer” refers to a macromolecule composed of repeating structuralunits connected by covalent chemical bonds or the polymerization productof one or more monomers, often characterized by a high molecular weight.The term polymer includes homopolymers, or polymers consistingessentially of a single repeating monomer subunit. The term polymer alsoincludes copolymers, or polymers consisting essentially of two or moremonomer subunits, such as random, block, alternating, segmented,grafted, tapered and other copolymers. Useful polymers include organicpolymers or inorganic polymers that may be in amorphous, semi-amorphous,crystalline or partially crystalline states. Crosslinked polymers havinglinked monomer chains are particularly useful for some applications.Polymers useable in the methods, devices and components include, but arenot limited to, plastics, elastomers, thermoplastic elastomers,elastoplastics, thermoplastics and acrylates. Exemplary polymersinclude, but are not limited to, acetal polymers, biodegradablepolymers, cellulosic polymers, fluoropolymers, nylons, polyacrylonitrilepolymers, polyamide-imide polymers, polyimides, polyarylates,polybenzimidazole, polybutylene, polycarbonate, polyesters,polyetherimide, polyethylene, polyethylene copolymers and modifiedpolyethylenes, polyketones, poly(methyl methacrylate),polymethylpentene, polyphenylene oxides and polyphenylene sulfides,polyphthalamide, polypropylene, polyurethanes, styrenic resins,sulfone-based resins, vinyl-based resins, rubber (including naturalrubber, styrene-butadiene, polybutadiene, neoprene, ethylene-propylene,butyl, nitrile, silicones), acrylic, nylon, polycarbonate, polyester,polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyolefinor any combinations of these.

“Elastomeric stamp” and “elastomeric transfer device” are usedinterchangeably and refer to an elastomeric material having a surfacethat can receive as well as transfer a material. Exemplary conformaltransfer devices useful in some methods of the invention includeelastomeric transfer devices such as elastomeric stamps, molds andmasks. The transfer device affects and/or facilitates material transferfrom a donor material to a receiver material. In an embodiment, a methodof the invention uses a conformal transfer device, such as anelastomeric transfer device (e.g. elastomeric stamp) in a microtransferprinting process, for example, to transfer one or more singlecrystalline inorganic semiconductor structures, one or more dielectricstructures and/or one or more metallic conductor structures from afabrication substrate to a device substrate.

“Elastomer” refers to a polymeric material which can be stretched ordeformed and returned to its original shape without substantialpermanent deformation.

Elastomers commonly undergo substantially elastic deformations. Usefulelastomers include those comprising polymers, copolymers, compositematerials or mixtures of polymers and copolymers. Elastomeric layerrefers to a layer comprising at least one elastomer. Elastomeric layersmay also include dopants and other non-elastomeric materials. Usefulelastomers include, but are not limited to, thermoplastic elastomers,styrenic materials, olefinic materials, polyolefin, polyurethanethermoplastic elastomers, polyamides, synthetic rubbers, PDMS,polybutadiene, polyisobutylene, poly(styrene-butadiene-styrene),polyurethanes, polychloroprene and silicones. In some embodiments, anelastomeric stamp comprises an elastomer. Exemplary elastomers include,but are not limited to silicon containing polymers such as polysiloxanesincluding poly(dimethyl siloxane) (i.e. PDMS and h-PDMS), poly(methylsiloxane), partially alkylated poly(methyl siloxane), poly(alkyl methylsiloxane) and poly(phenyl methyl siloxane), silicon modified elastomers,thermoplastic elastomers, styrenic materials, olefinic materials,polyolefin, polyurethane thermoplastic elastomers, polyamides, syntheticrubbers, polyisobutylene, poly(styrene-butadiene-styrene),polyurethanes, polychloroprene and silicones. In an embodiment, apolymer is an elastomer.

“Young's modulus” is a mechanical property of a material, device orlayer which refers to the ratio of stress to strain for a givensubstance. Young's modulus may be provided by the expression:

$\begin{matrix}{{E = {\frac{({stress})}{({strain})} = {( \frac{L_{0}}{\Delta\; L} )( \frac{F}{A} )}}},} & (I)\end{matrix}$where E is Young's modulus, L₀ is the equilibrium length, ΔL is thelength change under the applied stress, F is the force applied, and A isthe area over which the force is applied. Young's modulus may also beexpressed in terms of Lame constants via the equation:

$\begin{matrix}{{E = \frac{\mu( {{3\;\lambda} + {2\;\mu}} )}{\lambda + \mu}},} & ({II})\end{matrix}$where λ and μ are Lame constants. High Young's modulus (or “highmodulus”) and low Young's modulus (or “low modulus”) are relativedescriptors of the magnitude of Young's modulus in a given material,layer or device. In some embodiments, a high Young's modulus is largerthan a low Young's modulus, preferably about 10 times larger for someapplications, more preferably about 100 times larger for otherapplications, and even more preferably about 1000 times larger for yetother applications. In an embodiment, a low modulus layer has a Young'smodulus less than 100 MPa, optionally less than 10 MPa, and optionally aYoung's modulus selected from the range of 0.1 MPa to 50 MPa. In anembodiment, a high modulus layer has a Young's modulus greater than 100MPa, optionally greater than 10 GPa, and optionally a Young's modulusselected from the range of 1 GPa to 100 GPa. In an embodiment, a deviceof the invention has one or more components, such as substrate,encapsulating layer, inorganic semiconductor structures, dielectricstructures and/or metallic conductor structures, having a low Young'smodulus. In an embodiment, a device of the invention has an overall lowYoung's modulus.

“Inhomogeneous Young's modulus” refers to a material having a Young'smodulus that spatially varies (e.g., changes with surface location). Amaterial having an inhomogeneous Young's modulus may optionally bedescribed in terms of a “bulk” or “average” Young's modulus for theentire material.

“Low modulus” refers to materials having a Young's modulus less than orequal to 10 MPa, less than or equal to 5 MPa or less than or equal to 1MPa. In an aspect, the functional layer has a low modulus and thedelivery substrate has a higher Young's modulus, such as 10 times, 100times, or 1000 times larger than the functional layer Young's modulus.

“Bending stiffness” is a mechanical property of a material, device orlayer describing the resistance of the material, device or layer to anapplied bending moment. Generally, bending stiffness is defined as theproduct of the modulus and area moment of inertia of the material,device or layer. A material having an inhomogeneous bending stiffnessmay optionally be described in terms of a “bulk” or “average” bendingstiffness for the entire layer of material.

An example of a device is schematically illustrated in FIG. 9. Theelectronic device 10 comprises a thin elastomeric substrate 20 with aninner surface 30 and an outer surface 40. An array of functionalelectronic devices 50 is illustrated as supported by the inner surface30. The array comprises various device components, such as a flexibleand stretchable interconnect in a curved configuration 45. The innersurface 30 defines an enclosure 60, having a characteristic dimensionsuch as diameter 70 or length 80 between ends 90 and 95, or volume.Interior portion 60 is considered a closed volume as the substrate 20does not have unbound ends that freely moved. Instead, movement of ends80 and 90 are constrained. If ends 80 and 90 are able to freely move(such as if the tube were longitudinally cut), the device is consideredto have an open-tube volume. Interior portion 60 can accommodate anobject having a curved surface, even an irregular shaped object such asfinger. Preferably, diameter 70 is slightly smaller than the maximumdiameter of the object that is being received by the interior portion60. Such a size difference requires the substrate 20 to stretch toreceive the object, thereby ensuring tight conformal contact between thesubstrate 20, functional electronic devices 50, and the object surfacewithin interior portion 60. For clarity, devices 50 are not shown on theouter surface 40. As explained further in Example 1, however, innersurface devices 50 may be provided by first printing functionalelectronic devices to the outer surface 40. The substrate surfaces maythen be physically flipped, with the outer becoming the inner, and viceversa, to obtain the electronic device 10 illustrated in FIG. 9.

Example 1: Silicon Nanomembranes for Fingertip Electronics

This example relates to the use of semiconductor nanomaterials, advancedfabrication methods and unusual device designs for a class ofelectronics capable of integration onto the inner and the outer surfacesof thin, elastomeric sheets in closed-tube geometries, specially formedfor mounting on the fingertips. Multifunctional systems of this typeallow electrotactile stimulation with electrode arrays multiplexed usingsilicon nanomembrane (Si NM) diodes, high-sensitivity strain monitoringwith Si NM gauges, and tactile sensing with elastomeric capacitors.Analytical calculations and finite element modeling of the mechanicsquantitatively capture the key behaviors during fabrication/assembly,mounting and use. The results provide design guidelines that highlightthe importance of the NM geometry in achieving the required mechanicalproperties. This type of technology is compatible with applicationsranging from human-machine interfaces to ‘instrumented’ surgical glovesand many others.

Electrotactile stimulators and tactile sensors are of interest asbi-directional information links between a human operator and a virtualenvironment, in a way that could significantly expand function intouch-based interfaces to computer systems, with applications insimulated surgery, therapeutic devices, robotic manipulation and others[1-5]. Electrotactile stimulation allows information to be presentedthrough the skin, as an artificial sensation of touch, commonlyperceived as a vibration or tingling feeling [6,7]. Such responsesmanifest through the excitation of cutaneous mechanoreceptors as aresult of passage of a suitably modulated electrical current into thetissue [8]. Developed originally in the 1950's and further advanced inthe 1970's, electrotactile stimulation has been traditionally exploredfor programmable braille readers and displays for the visually impairedas well as for balance control in individuals who suffer from vestibulardisorders [5,9-12]. Tactile sensors, on the other hand, measure pressurecreated by physical contact, in a way that provides complementaryinformation for potential use in feedback loops with the electrotactileprocess. Additional classes of sensors that can be important in thiscontext include those for motion and temperature. Incorporating suchtechnologies into a conformal, skin-like device capable of intimate,non-invasive mounting on the fingertips might, therefore, represent auseful achievement. Recent advances in flexible and stretchableelectronics create opportunities to build this type of device [13-17].

Disclosed herein are materials, fabrication strategies and devicedesigns for ultrathin, stretchable silicon-based electronics and sensorsthat can be mounted on the inner and outer surfaces of elastomericclosed-tube structures for integration directly on the fingertips. Theactive components and interconnects incorporate advanced mechanicsdesigns, capable of accommodating large strains induced not only bynatural deformations of the tubes during use, but also during a criticalstep in the fabrication process in which the tubes, specially formed tomatch the shapes of fingertips, are flipped inside-out. This‘flipping-over’ process allows devices initially mounted on the outersurface of the tube to be reversed to the inner surface, where they canpress directly against the skin when mounted on the fingers. Analyticalcalculations and finite element modeling (FEM) provide quantitativeinsights into design layouts that avoid plastic deformation or fracture.We demonstrate these concepts in multifunctional fingertip devices thatinclude electrotactile electrode arrays multiplexed with Si nanomembrane(NM) diodes, strain sensors based on Si NM gauges, and tactile sensorarrays that use capacitors with low-modulus, elastomeric dielectrics.

FIG. 1 schematically illustrates steps for integrating devices based onSi NMs in stretchable, interconnected geometries with elastomericsubstrates, following adapted versions of procedures described elsewhere[13,18]. The fabrication uses a Si wafer with a 100 nm thick coating ofpolymethylmethacrylate (PMMA) as a temporary substrate for the initialparts of the process. A layer of polyimide (PI; 1.25 μm thick) formed byspin coating a poly (amic acid) precursor and baking in an inertatmosphere at 250° C., serves as the support for the devices.Electronically active materials are deposited (e.g. metallization) ortransfer printed (e.g. Si NMs) onto the PI and patterned byphotolithography and etching. Another layer of PI (1.25 mm thick) spincast and cured on top of the device layers provides encapsulation andlocates the devices near the neutral mechanical plane (NMP). Next,patterned reactive ion etching through the entire multilayer stack (i.e.PI/devices/PI) defines an open mesh structure. This same process removesPI in regions of the electrotactile stimulation electrodes, to allowdirect contact with the skin. Immersion in an acetone bath washes awaythe underlying PMMA, thereby allowing the entire mesh to be lifted off,in a single piece, onto the surface of a flat slab ofpolydimethylsiloxane (PDMS), using procedures described previously[19,20]. Evaporating a layer of SiO₂ onto the mesh/PDMS and exposing thesilicone target substrate (Ecoflex 0030, Smooth-On, Inc.) to UV-ozone(to creating reactive —OH groups the surface) enables bonding betweenthe two upon physical contact [21]. (Low pressures avoid contact betweenthe PDMS and the finger-tube, thereby allowing bonding only to themesh.) Removal of the stamp completes the transfer process, as shown inFIG. 1 c.

The electrotactile electrodes use 600 nm thick layers of Au in aconcentric design, consisting of an inner disk (400 μm radius)surrounded by an outer ring (1000 μm radius) with a 250 μm wide gapbetween the two. Interconnects consist of 100 μm wide traces of Au inserpentine geometries (radii of curvature ˜800 μm); these traces connectthe electrotactile electrodes to Si NM diodes (lateral dimensions of 225μm×100 μm and thicknesses of 300 nm). Two layers of Au interconnects(200 nm and 600 nm thick), isolated by a 1.25 μm PI layer and connectedthrough etched PI vias, establish a compact wiring scheme with overlyinginterconnects. The 600 nm thick Au interconnect layer allowed robustelectronic contact though the PI vias. The strain gauge arrays consistof four Si NMs (strips with lateral dimensions of 1 mm×50 μm andthicknesses of 300 nm) electrically connected by 200 nm thick, 60 μmwide Au traces patterned in serpentine shapes (radii of curvature ˜400μm). The tactile sensors use 200 nm thick Au electrodes andinterconnects in the geometry of the electrotactile arrays but with theconcentric electrode pairs replaced by single, disc-shaped electrodes(radii ˜1000 μm).

The Ecoflex substrates, which we refer to as finger-tubes, adopt threedimensional forms specifically matched to those of fingers on a plasticmodel of the hand. The fabrication involves pouring a polymer precursorto Ecoflex onto a finger of the model and curing at room temperature for1 hour, to create a conformal sheet with ˜125 μm thickness. Pouring asecond coating of precursor onto this sheet and curing for an additional1 hour doubles the thickness; repeating this process 4 times results ina thickness of ˜500 μm. Removing the Ecoflex from the model andcompleting the cure by heating at 70° C. for 2 hours forms a freestanding structure, i.e. a finger-tube, like the one illustrated in FIG.2. Ecoflex is an attractive material for this purpose because it has alow modulus (˜60 kPa) and large fracture strain (˜900%). The formerallows soft, intimate contact with the skin; the latter enables the‘flipping-over’ process referred to previously, and described inquantitative detail in a following section. Transfer printing deliversthe device mesh structure to the outer surface of the finger-tube, whilepressed into a flattened geometry (FIG. 2b ). The entire integratedsystem is then flipped inside-out, to move the mesh from the outer tothe inner surface of the tube, as shown in FIG. 2c,d . Multifunctionaldevices incorporate electrotactile stimulators on the inside, and straingauge arrays and tactile sensors on the outside.

Device designs described previously have the advantage that they areconformal to the finger, in a way that naturally presses the electronicson the interior surface of the finger-tube (in this case theelectrotactile stimulating electrodes) into intimate contact with theskin. The flipping-over process represents a critical step, enabled bycareful design of the mechanics in the device mesh. Quantitativemechanics modeling provides important insights. The finger-tube can beapproximated as a self-equilibrated, axisymmetric tube with twodimensional symmetry. Energy minimization using linear elastic shelltheory determines the resulting shapes. FIG. 3a shows analytical and FEMresults for an Ecoflex cylinder with radius (R_(radial)) of 7.5 mm andthickness of 500 μm when bent back on itself, at a mid-way point duringthe flipping-over process. The minimum axial radius of curvature(R_(axial)) of 596 μm, as indicated in FIG. 3a , defines the location ofmaximum induced strain as the tube is flipped over. The maximum strainson the inner and outer surfaces in this configuration, as shown in thecolor map of FIG. 3b , are ˜30-40% (see supplementary file atstacks.iop.org/Nano). The device mesh structures must, therefore, beable to accommodate strains in this range. This requirement isnon-trivial for systems like the ones described here, due to theirincorporation of brittle materials such as silicon (fracture strain˜1%).

Circuit layouts, guided by theory, can be identified to satisfy theserequirements. As an example, FIG. 3c provides a diagram of a multiplexedelectrotactile array in a mesh configuration with narrow, serpentineinterconnects. The orange and blue regions correspond to Au layersseparated by layers of PI, respectively; the red regions indicate Si NM(300 nm thick) diodes in a PIN (p-doped/intrinsic/n-doped)configuration. The short dimensions of the diodes lie parallel to theflipping-over direction, to minimize strains in the Si during thisprocess. These optimizations lead to maximum calculated strains that areonly 0.051%, 0.10%, and 0.040% for the Au, PI, and the Si, respectively(see FIG. 3d ). The computed position of the NMP also appears in FIG. 3d. Since the moduli of the device layers are several orders of magnitudelarger than that of Ecoflex, the location of the NMP plane is largelyindependent of the Ecoflex. Appropriate selection of the thicknesses ofthe PI layers allows the NMP to be positioned at the location of the SiNMs, thereby minimizing the induced strains in this brittle material[21,22]. The thicknesses of the Si NM diodes influences the maximumstrains that they experience, as shown in analytical calculations ofFIG. 3f . A minimum occurs at the thickness that places the NMP at theshortest distance from the Si NM diode (i.e. h_(NMP)). The position ofthis minimum can also be adjusted by changing the thicknesses of the PIlayers, for example. Further reductions in strain can be realized byreducing the lengths of the devices. Implementing designs thatincorporate these considerations and exploiting interconnects withoptimized serpentine layouts ensures robust device behavior throughoutthe fabrication sequence. For example, FIG. 3e shows negligible changein the I-V characteristics (Agilent 4155C semiconductor parameteranalyzer) of a Si NM diode before and after the flipping-over process.

Experimental results demonstrate expected functionality in theelectrotactile arrays. FIG. 4a shows the perception of touch on a dryhuman thumb as a function of voltage and frequency, applied between theinner dot and outer ring electrodes (FIG. 3d ). Stimulation used amonophasic, square-wave with 20% duty cycle, generated using a customsetup. The inset provides an image of a device, with connection toexternal drive electronics via a flexible anisotropic conductive film(ACF). The required voltage for sensation decreases with increasingfrequency, consistent with equivalent circuit models of skin impedancethat involve resistors and capacitors connected in parallel. Theabsolute magnitudes of these voltages depend strongly on the skinhydration level, electrode design, and stimulation waveform [23]. FIG.4b shows I-V characteristics of an electrotactile electrode pair whilein contact with a hydrated human thumb, measured through a multiplexingdiode. At high positive voltages, the resistance of the diode isnegligible compared to the skin; here, the slope of the I-Vcharacteristics yield an estimate of the resistance of theskin-electrode contact plus the skin. The value (˜40 kΩ) is in a rangeconsistent with measurements using conventional devices [24,25]. Thediode is stable to at least 20 V, corresponding to currents of 0.25 mA,which is sufficient for electrotactile stimulation on the skin andtongue [2,6,7].

These diodes enable multiplexed addressing, according to an approachthat appears schematically in FIG. 4c . Each unit cell consists of onediode and one electrotactile electrode pair. FIG. 4d presents a table ofthe inputs required to address each of the six electrotactile channels.For example, channel S_(DA) can be activating by applying a highpotential (+5 V) to inputs A and E and a low potential (0 V) to inputsB, C, and D, thereby yielding a +5 V bias across the outer ring (+5 V)and inner ring electrode (0 V) of this channel. This configurationforward biases the Si NM diode, which results in stimulation current, asshown in FIG. 4b . At the same time, channels S_(EB) and S_(EC)experience a bias of −5 V across the electrodes but in these cases theSi NM diodes are reverse biased, thus preventing stimulating current.Channels S_(DE), S_(DC), and S_(EA) have the same potential on the innerand outer electrodes, resulting in zero bias. Electrical isolation ofadjacent channels is a consequence of inner to outer electrodeseparations (250 μm) that are small compared to the distances betweenchannels (6000 μm). Advanced multiplexing schemes that use severaldiodes per stimulation channel, or active transistors, are compatiblewith the fabrication process and design principles outlined here.

FIG. 5 shows a set of straight, uniformly doped Si NMs as strain gaugesaddressed with interconnects in a mesh geometry. FEM calculationssummarized in FIG. 5 reveal strain profiles in a 1×4 array of gauges(vertical strips; yellow dashed box and upper inset highlights anindividual device) on Ecoflex, under a uniaxial in-plane strain of 10%.These results show that the overall strain is mostly accommodated bychanges in the shapes of the serpentine interconnects and, of course,the Ecoflex itself. The Si NM gauges experience strains (˜10 ⁻³) thatare ten times lower than the applied strain, as shown in the inset inFIG. 5 a.

The ability to use Si NMs as high performance strain gauges instretchable forms results from the strong piezoresistance properties ofSi, combined with serpentine layouts. These characteristics, takentogether, determine the fractional change in resistance per appliedstrain. The associated effective gauge factor (GF_(eff)) can be relatedto the intrinsic gauge factor of a silicon gauge, GF_(Si)=ΔR/(R∈_(Si))where ΔR is the change in resistance, R is the initial resistance, and∈_(Si) is the strain in the silicon, by the following expressionGF_(eff)=GF_(Si)(∈_(Si)/∈_(app)) where ∈_(app) is the strain applied tothe overall, integrated system. The designs reported here yield valuesof ∈_(Si)/∈_(app) that are much smaller than one, specifically to avoidfracture-inducing strains in the Si during fabrication, mounting and useover physiologically relevant ranges of strain. FIG. 5b showsexperimentally measured values of ΔR (evaluation at 1 V, using anAgilent 4155C semiconductor parameter analyzer) as a function of∈_(app), which corresponds to GF_(eff)˜1. By fitting the experimentaland FEM results to FIG. 5b , the GF_(Si) is ˜95, consistent with arecent report on Si NM strain gauges, with otherwise similar designs, onflexible sheets of plastic [26]. We emphasize that device designparameters, such as the size of the gauge and the dimensions of theserpentine interconnects, enable engineering control over GF_(eff), fromvalues as large as GF_(Si) to those that are much smaller, with acorrespondingly increased range of strains over which measurements arepossible.

FIG. 5c shows a strain gauge array on a finger-tube located near theknuckle region of the thumb, in straight (I) and bent (II) positions.Upon bending, the gauges experience tensile strain, resulting in anincrease in resistance, as shown for three bending cycles in FIG. 5d .The relative resistance changes suggest that the strain associated withbending reaches ˜6%. As expected, side-to-side motions induced nochanges. FIG. 5e shows a similar array on a thin sheet of Ecoflex,mounted near the metacarpal region of the thumb. Here, the deviceadheres to the skin by van der Waals interactions, similar to mechanismsobserved in epidermal electronic systems [13]. The images in FIG. 5ecorrespond to the thumb in straight (III) and sideways deflected (VI)positions. The changes in resistance for the two gauges on opposite endsof the 1×4 array for three side-to-side cycles of motion appear in FIG.5f . For each cycle, the change in resistance of the rightmost gaugeindicates compressive strain; the leftmost indicates correspondingtensile strain. The results suggest that arrays of gauges can be used toidentify not only the magnitude but also the type of motion.

As a final demonstration, we built a type of tactile (pressure) sensorsuitable for integration on the finger-tube platform. The devicesexploit changes in capacitance associated with opposing electrodes onthe inner and outer surfaces of the Ecoflex. Applied pressure decreasesthe thickness of the Ecoflex, thereby increasing the capacitance of thisstructure. Here, layouts like those for the electrotactile devices serveas inner electrodes; a mirror image of this array mounted in an alignedconfiguration on the outer surface defines a collection of parallelplate capacitors with the Ecoflex as the dielectric. An array of suchdevices on the anterior surface of a model of the hand appears in FIG.6a . FIGS. 6b and 6c show images of the inner and outer electrodearrays. The relative change in capacitance with applied pressure for arepresentative device appears in FIG. 6d (black symbols). Here,capacitance was measured (Agilent E4980A LCR meter) as a function ofpressure applied with a series of weights mounted on a platform with aconstant contact area, taking care to minimize effects of parasiticcapacitances and to eliminate ground loops. Approximately linearbehavior is observed over the range studied, consistent with simplemechanical models, ΔC/C_(o)=P/(Ē_(Ecoflex)−P), where ΔC is thecapacitance change, C_(o) is the initial capacitance, P is the appliedpressure, and Ē_(Ecoflex) is the effective Ecoflex modulus. This simplemodel assumes no electrostriction or strain induced changes indielectric force (FIG. 6d , black line). Due to the Poisson effect, thedevices also respond to in-plane strains (∈_(applied)), as shown in FIG.6d (red), consistent with the simple modelΔC/C_(o)=[(EA)_(system)/(EA)_(electrodes)]v∈_(applied), where thePoisson's ratio (v) is 0.496, and (EA)_(system) and (EA)_(electrodes)are the tensile stiffness of the system and electrodes respectively.This type of technology provides a simple alternative to recentlyreported devices that offer similar functionality, but on flexiblesubstrates, and based on conductive elastomers, elastomeric dielectrics,or compressible gate dielectrics in organic transistors. [14, 16, 18,27, 28].

The results presented here establish some procedures and design rulesfor electronics and sensors that can be mounted conformally onto thefingers. Other appendages of the body can be addressed in similarmanner. Furthermore, most of the considerations in mechanics andfabrication are agnostic to the specific device functionality ormounting locations. As a result, many of these concepts can be appliedgenerally, to other types of systems and modes of use. Future challengesinclude the development of capabilities for wireless power supply anddata transfer.

Example 2: Methods of Making the Electronic Devices

1. Electrotactile Arrays:

a. Cut 1′×1′ SOI wafers ((110), 300 nm Si) and clean with acetone andIPA.

b. Form a 900 nm layer of SiO₂ by PECVD as p-dope diffusion mask.

c. Pattern diffusion mask by: i. Pattern photoresist (PR) AZ5214: Spincoat PR AZ5214 (3000 rpm, 30 s), pre-bake (110° C., 1 min), align maskand expose, develop with MIF327 (40 s), post-bake (110° C., 3 min). ii.Wet etch with buffered oxide etchant (BOE) (NH4F:HF=6:1) for 1.5 min andremove PR with acetone.

d. P-type doping: i. Clean wafers with Nano-strip™ (Cyantek), place nextto boron doping source, and put into furnace (1000° C.) for 30 min. ii.Etch SiO₂ mask completely with HF (30 sec), and form another 900 nmlayer of SiO₂ by PECVD as n-dope diffusion mask. iii. Pattern diffusionmask: Same as 1c.

e. N-type doping: i. Clean wafers with Nano-strip™, place next tophosphorous doping source at 1000° C. for 10 min. ii. Etch SiO₂ maskcompletely with HF (30 sec).

f. Create holes (3 μm dia., spacing 30 μm) for releasing Si film: i.Spin coat PR Shipley S1805 (3000 rpm, 30 s), pre-bake (110° C., 1 min),align mask and expose, develop with MIF327 (9 s), post-bake (110° C., 3min). ii. Etch Si with RIE (50 mtorr, 40 sccm SF6, 100 W, 1 min).

g. Undercut oxide layer of SOI: i. Immerse wafers in HF solution for15-20 min until the Si layer is detached from the substrate.

h. Pick up the Si film from the SOI wafer with a PDMS stamp.

i. Prepare target Si wafer: i. Spin coat Si wafer withpolymethylmethacrylate (PMMA, 3000 rpm, 30 s, ˜100 nm), cure at 180° C.for 1.5 min. ii. Spin coat polyimide precursor (4000 rpm, 30 s) andpartially cure at 150° C. for 40 sec.

j. Transfer Si to target Si wafer: i. Press the stamp into contact withthe target wafer and apply force with hands for 10 s. ii. Put stamp andtarget wafer on a hotplate at 110° C. and slowly release the stamp whenthermal expansion of the stamp is observed. iii. Put target wafer (nowwith Si film) on hotplate at 150° C. for another 5 min and remove PRwith acetone (2 s). iv. Bake in an inert atmosphere at 250° C. for 1 hr.

k. Si diode isolation: i. Pattern PR AZ5214. ii. Etch exposed Si withRIE (50 mtorr, 40 sccm SF6, 100 W, 1 min) and strip PR with acetone.

l. 1st Au interconnect layer: i. Deposit Cr (5 nm)/Au (200 nm) withelectron beam evaporator. ii. Pattern PR AZ5214. iii. Wet etch Au andCr. iv. Strip PR with acetone.

m. PI insulation layer with vias: i. Spin coat polyimide precursor (4000rpm, 30 s). ii. Prebake on hotplate (150° C., 5 min). iii. Bake in aninert atmosphere at 250° C. for 1 hr. iv. Spin coat PI with PR AZ4620(3000 rpm, 30 s), pre-bake (110° C., 1 min), align via mask and expose,develop with 3:1 diluted MIF400 (40 s). v. Etch exposed polyimide withRIE (100 W, 150 mTorr, 20 sccm 02, 20 min). vi. Strip PR with acetone.

n. 2_(nd) Au interconnect layer: i. Deposit Cr (10 nm)/Au (600 nm) withelectron beam evaporator. ii. Pattern PR AZ5214. iii. Wet etch Au andCr. iv. Strip PR with acetone.

o. Final PI encapsulation and etch: i. Form PI layer: Same as 1n. ii.Pattern PR AZ4620. iii. Etch exposed polyimide with RIE (100 W, 150mTorr, 20 sccm 02, 50 min) to form PI mesh structure. iv. Strip PR withacetone.

p. Transfer printing: i. Immerse device in heated acetone bath (100° C.)to undercut PMMA. ii. Press PDMS stamp into contact with the device andquickly remove to transfer device onto the stamp. iii. Deposit Cr (5nm)/SiO₂ (20 nm) with e-beam evaporator. iv. Ultra-violet/ozone (UV-O)treat the target substrate (Ecoflex finger tube) for 4 min. v. Press thePDMS stamp onto Ecoflex and remove stamp slowly.

2. Strain Gauge Arrays:

a. Cut 1′×1′ (110) SOI wafers (300 nm Si) and clean with acetone andIPA.

b. P-type doping: same as 1d with a 4 min doping time.

c. Transfer print Si to target wafer: same as 1f-j.

d. Si strain gauge isolation: same as 1k.

e. Au interconnect layer: same as 1l.

f. Final encapsulation: same as 1o with 30 min O₂ RIE.

g. Transfer printing: same as 1p.

3. Contact Sensor Array:

a. Cut 1′×1′ Si wafers and clean with acetone and IPA.

b. Spin coat PMMA (3000 rpm, 30 s) as sacrificial layer.

c. Form polyimide layer as substrate: Same as 1m.

d. Au interconnect layer: same as 1l.

e. Final encapsulation: same as 2f.

f. Transfer printing to overlay with electrotactile electrodes: same as1p.

Summaries of various methods for making sensors and actuators useful inthe devices and methods provided herein are summarized in FIGS. 10-13.

Mechanics Modeling:

Strain of the multiplexed electrotactile arrays during the flipping-overprocess. The elastomeric Ecoflex finger-tube with the thickness t_(sub)is flipped over twice on the finger model with the radius R_(finger).FIG. 8 illustrates a self-equilibrated, axisymmetric Ecoflex tube duringthe flipping-over process; AB represents the cylindrical portion incontact with the surface of plastic hand; the outer surface DE is alsocylindrical; transition between the two can be approximated by asemi-circle BC (with radius R₁ to be determined in FIG. 8) and asinusoidal curve CD (with half wavelength L to be determined). For theprofile shown in FIG. 8, the linear elastic shell theory gives thebending energy and the membrane energy. Minimization of the total energythen gives R₁ and L. For R_(finger)=7.5 mm and t_(sub)=500 μm, energyminimization gives the bending radius R₁=596 μm and L=2.47 mm for thePoisson's ratio of Ecoflex v=0.496. The maximum tensile and compressivestrains in Ecoflex are ∈_(tensile)=34.4% and ∈_(compressive)=−49.5%,which agree well with the FEM results (∈_(tensile)=35.1% and∈_(compressive)=−46.9%).

The multiplexed electrotactile arrays are modeled as a composite beamwith multiple layers. The bending moment and membrane force obtainedfrom the above analytical model are imposed on the multiplexedelectrotactile arrays. This gives the analytical expressions of themaximum strain in Si and Au, which are validated by FEM for relativelylong Si diodes. For relatively short Si diodes, the analyticalexpressions overestimate the maximum strain in Si and Au.

Mechanical analysis of the tactile (pressure) sensor: The inner dot andouter ring electrodes form pairs of parallel capacitors. The capacitancechange is related to the applied pressure that results in the decreaseof the thickness of Ecoflex dielectric

$\begin{matrix}{{\frac{\Delta\; C}{C_{0}} = \frac{P}{{\overset{\_}{E}}_{ecoflex} - P}},} & ({S1})\end{matrix}$where: Ē_(ecoflex)=(1−v)E/[(1+v)(1−2v)]is the effective modulus of Ecoflex dielectric under uniaxialstretching, and E=60 kPa is the Young's modulus of Ecoflex. As shown inFIG. 6d , Eq. (51) agrees well with experiments.

For an applied tensile strain ∈_(applied), the strain in the Ecoflexdielectric between electrodes is related to the tensile stiffness(EA)_(system) of the system and tensile stiffness (EA)_(electrodes) ofthe electrodes by ∈_(applied)(EA)_(system)(EA)_(electrodes). Thecapacitance change of a single element of the pressure sensor array isalso determined by the decrease of the thickness of the Ecoflexdielectric, and is given by

$\begin{matrix}{\frac{\Delta\; C}{C_{0}} = {\frac{({EA})_{system}}{({EA})_{electrodes}}v\;{ɛ_{applied}.}}} & ( {S\; 2} )\end{matrix}$

References for Examples 1-2

-   1. Barfield W, Hendrix C, Bjorneseth O, Kaczmarek K A and Lotens W    1995 Presence-Teleoperators and Virtual Environments 4 329-   2. Matteau I, Kupers R, Ricciardi E, Pietrini P and Ptito M 2010    Brain Research Bulletin 82 264-   3. Tan H Z, Durlach N I, Reed C M and Rabinowitz W M 1999 Perception    & Psychophysics 61 993-   4. Sparks D W, Kuhl P K, Edmonds A E and Gray G P 1978 Journal of    the Acoustical Society of America 63 246-   5. Danilov Y P, Tyler M E and Kaczmarek K A 2008 International    Journal of Psychophysiology 69 162-   6. Kaczmarek K A, Webster J G, Bachyrita P and Tompkins W J 1991    Ieee Transactions on Biomedical Engineering 38 1-   7. Lozano C A, Kaczmarek K A and Santello M 2009 Somatosens. Mot.    Res. 26 50-   8. Warren J P, Bobich L R, Santello M, Sweeney J D and Tillery S I H    2008 Ieee Transactions on Neural Systems and Rehabilitation    Engineering 16 410-   9. Bach-y-Rita P, Tyler M E and Kaczmarek K A 2003 International    Journal of Human-Computer Interaction 15 285-   10. Jones L A and Safter N B 2008 Human Factors 50 90-   11. Vuillerme N, Pinsault N, Chenu O, Demongeot J, Payan Y and    Danilov Y 2008 Neuroscience Letters 431 206-   12. Vidal-Verdu F and Hafez M 2007 Ieee Transactions on Neural    Systems and Rehabilitation Engineering 15 119-   13. Kim D H et al. 2011 Science 333 838-   14. Lipomi D J, Vosgueritchian M, Tee B C, Hellstrom S L, Lee J A,    Fox C H and Bao Z 2011 Nature Nanotech. 6 788-   15. Rogers J A and Huang Y G 2009 Proc. Natl. Acad. Sci. U.S.A 106    16889-   16. Someya T, Sekitani T, Iba S, Kato Y, Kawaguchi H and Sakurai T    2004 Proc. Natl. Acad. Sci. U.S.A 101 9966-   17. Rogers J A, Lagally M G and Nuzzo R G 2011 Nature 477 45-   18. Kim D H et al. 2011 Nat. Mater. 10 316-   19. Meitl M A et al. 2006 Nat. Mater. 5 33-   20. Yu J and Bulovic V 2007 Appl. Phys. Lett. 91-   21. Kim D H et al. 2008 Science 320 507-   22. Rogers J A, Someya T and Huang Y G 2010 Science 327 1603-   23. Kaczmarek K A and Haase S J 2003 Ieee Transactions on Neural    Systems and Rehabilitation Engineering 11 9-   24. Woo E J, Hua P, Webster J G, Tompkins W J and Pallasareny R 1992    Medical & Biological Engineering & Computing 30 97-   25. Hua P, Woo E J, Webster J G and Tompkins W J 1993 Ieee    Transactions on Biomedical Engineering 40 335-   26. Won S M et al. 2011 Ieee Transactions on Electron Devices 58    4074-   27. Someya T et al. 2005 Proc. Natl. Acad. Sci. U.S.A 102 12321-   28. Takei K et al. 2010 Nat. Mater. 9 821

Example 3: Appendage Mountable Electronic Devices Conformable toBiological Surfaces

One example of an appendage mountable electronic system is schematicallysummarized in FIGS. 14-17, including an appendage corresponding to afinger or a finger-tip. Different views of an appendage mountableelectronic system 10 is provided in FIG. 14(A-C), with a top view (A), aside cross-section view (B) and a cross-section viewed from an end (C).Referring to the different views of FIG. 14, the system 10 comprises aflexible and stretchable substrate 20 having an inner surface 30 and anouter surface 40. In this example, the electronic device 50 comprises aplurality of flexible or stretchable sensors 54 supported by the outersurface 40, and a plurality of flexible or stretchable actuators 55supported by the inner surface 30. The electronic device furthercomprises various components to provide desired functionality andoperating characteristics. For example, FIG. 14 illustrates electricalinterconnects 53 in a curved or serpentine configuration thatelectrically interconnect more rigid components (e.g., rigid deviceislands), such as electrodes 54 having an interior disk-shaped electrodepositioned within and concentric to a ring-shaped electrode. Thecross-sectional views provided in FIGS. 14B and 14C illustrate thatelectronic device 50 may be supported by the inner surface 30, the outersurface 40, or by both surfaces. Optionally, the electronic device maycomprise an array of sensors 54, such as tactile sensors, supported bythe outer surface and an array of stimulators 55, such as electrotactilestimulators, supported by the inner surface 30, for interfacing with asurface of an appendage.

An enclosure 60 is defined by inner surface 30. Referring to FIG. 15,enclosure 60 receives an appendage 61 such that a surface 62 of theappendage is in conformal contact with the inner surface 30 of thesubstrate 20. FIG. 15 illustrates electronic device 50 on the outersurface 40 that is a system 10 with outer surface supported sensors,such as tactile sensors, for assessing a tactile parameter such ascontact force or pressure with external surface 63. Optionally, thesubstrate 20 may stretch to accommodate the appendage 61 within theenclosure 60. Optionally, the enclosure does not stretch to accommodatean appendage.

For comparison, FIG. 16 shows a system 11 having electronic devicessupported on the inner surface 30 of the substrate 20. The electronicdevices may be electrotactile stimulators that interface with livingtissue of an appendage within the enclosure, or a sensor to measure aparameter of interest of the appendage (e.g., temperature, hydration).The panels on the right side of FIGS. 15-16 indicate an aspect where theshape of the enclosure changes upon receipt of the appendage asillustrated by an end view cross-section of the system 10. As desired,one or more barrier or encapsulation layers 21 may encapsulate at leasta portion of the electronic device, such as the sensors and/oractuators, including those supported by the outer surface (illustratedin top right panel of FIG. 15) and/or those by the inner surface.

One useful aspect of outer surface mounted sensors is for interfacingwith an external surface 63. For a sensor 54 that is a tactile sensor,the tactile sensor interface provides a measure of the contact force orpressure between the sensor 54 and the external surface 63. For othersensor types, such as temperature, optical, pH or any others disclosedherein, the sensor provides an output corresponding to the functionalityof the sensor. This is generally referred to as “external interfacing”or an external interface parameter and is indicated by 64. In contrast,referring to FIG. 16, actuators 55 supported by the inner surface mayinterface with living tissue of an appendage within the enclosure. Thisis generally referred to as “internal interfacing” or an internalinterface parameter. In an aspect, any of the systems provided hereinare for external interfacing (FIG. 15), internal interfacing (16), orboth external and internal interfacing (combination of FIGS. 15 and 16,as indicated by the electronic devices in FIGS. 14B and C).

One example of a method for making any of the devices provided herein isschematically illustrated in FIG. 17. FIG. 17A shows an appendagemountable electronic system 10 having an electronic device 50 supportedon the substrate 20 outer surface 40 with inner surface 30 defining anenclosure 60. The enclosure 60, may be described by a characteristicdimension such as diameter 70 or length between ends 90 and 95, orvolume of 60. In an embodiment, diameter 70 is slightly smaller than themaximum diameter of the object that is being received by the interiorportion 60. Such a size difference requires the substrate 20 to stretchto receive the object, thereby ensuring tight conformal contact betweenthe substrate 20, electronic devices 50, and the appendage surfacewithin interior portion enclosure 60 (see, e.g., FIGS. 15-16).

FIG. 17B illustrates application of a substrate surface flipping force210 that flips outer surface 40 to the inner surface 41 and,correspondingly, inner surface 30 to outer surface 31, as illustrated inFIG. 17C. FIG. 17D indicates that new outer surface may receive anotherelectronic device, such that a first array 271 of devices is supportedby the outer surface and a second array 272 of devices is supported bythe inner surface, such as to provide a multifunctional system 12.

FIG. 18 is a process flow summary of one embodiment for making any ofthe systems disclosed herein. In step 1800 a flexible and stretchablesubstrate is provided, such as having an enclosure defined by thesubstrate inner surface. An electronic device is provided to thesubstrate outer surface 1810. The device may be partially encapsulatedby a barrier layer. Depending on the application of interest, anappendage may be placed in the enclosure, as outlined in 1820. Thisdevice may then be used to interface with an object that is external tothe enclosure, such as for surface sensing applications. Alternatively,if the system is for an application to interface with the appendage,flipping 1830 may be performed, so that the electronic device is on theinner surface. If only interfacing with the appendage is desired, step1840 is followed. Alternatively, another electronic device may beprovided to the outer surface as indicated in 1850, which is optionallyat least partially or completely encapsulated with a barrier layer. Inthis fashion, dual functionality is obtained for external and internalinterfacing 1860. In contrast, 1820 is for external interfacing only,and 1840 is for internal interfacing only. As outlined herein, any ofthe electronic devices are provided to a surface such as by transferprinting of various metallic and semiconductor components, preferablythin components in a layout that can accommodate bending and stretching.

FIG. 20 is a process flow summary of another embodiment for making anyof the systems disclosed herein by providing an object 1900 thatcorresponds to the appendage, or model or mold thereof. An electronicdevice is provided to the surface of the object 1910. A prepolymer orother substrate-precursor is cast against the object surface and theelectronic device 1920. Depending on the application of interest, thedevice is then ready for use 1930 or may receive another electronicdevice on the outer substrate 1940. As indicated by steps 1950 1960 and1970, the printing to the external surface can be before or afterremoval from the object provided in step 1910.

Example 4: Tactile Sensor on External and Internal Surfaces

In another example, any of the systems provided herein has electronicdevices on both the inner and outer surfaces, wherein the inner andouter surface devices are in communication with each other such as tofunctionally provide a pressure or force sensor. In one embodiment, thecommunication is an electrical communication for a pair of opposedelectrodes. Another example of functional communication include directelectrical contact, where output from a device on one surface isprovided to a device on the outer surface. In another aspect, thedevices are in thermal contact with each other, such as between a heatsource and a thermal or temperature sensor.

An aspect of the invention is a tactile sensor that provides informationabout contact forces or pressures based on a change in thickness of amaterial between two opposed electrodes. Examples include pressuresensors based on capacitance or thermal sensing. Referring to FIG. 19, afirst electronic device 610 and a second electronic device 620 aresupported by inner and outer surfaces of elastomeric substrate 20. Forsimplicity, only a portion of a side-view cross-section of the system isillustrated in FIG. 19, with an enclosure volume for conformallycontacting an appendage (not shown) adjacent to an array of firstelectronic device 610. For simplicity, FIG. 19 exemplifies electronicdevices that are electrodes 610 and 620. Electrical interconnects 640(first plurality of electrical interconnects) and 650 (second pluralityof electrical interconnects) provide an electrical connection, eitherindependently or in a multiplexed configuration, to each electrode. Theinterconnects may be in a bent configuration, such as serpentinegeometry. The interconnects may be embedded within first and secondencapsulation layers 660 670, respectively. Optionally, a barrier layer680 is used to further electrically isolate the interconnects from eachother and/or the surrounding environment. The barrier layer andencapsulation layers positions are determined in part by the desiredapplication. For example, a barrier layer that is a thermal barrier maybe positioned between a thermal source/thermal sensor and theappendage/external environment, depending on positions of the senor andsource.

Electronic devices, e.g., thermal sensors/sources or electrodes 610 and620 may be spatially aligned with respect to each other and separated byelastomeric substrate 20 of a defined thickness 630, therebyfunctionally forming a capacitor whose capacitance varies with thickness630. In this manner, a pressure or force sensor is provided thatmeasures pressure or force based on a change in the thickness 630. Inthis aspect, it is important that substrate 20 be formed of an elasticmaterial that will change thickness in accordance with an appliedcontact force or pressure. Preferably, the material is elastomeric inthat its response characteristics are reversible and will compress andrelax back to an uncompressed state with minimal change in restingthickness. Elastomeric materials can help provide more accurate, robustand reliable measure of force or pressure. Force and pressure aregenerally used interchangeably in that one can be calculated from theother based on the expression F=P/A, where F is the force (Newtons), Pis the pressure (Pascals) and A is the area over which the pressure isapplied (m²). Functionally, a thermal-based system is similarlyarranged, except decrease in thickness results in increase intemperature. Similarly, optical sources and detectors may be employed,where optical transmission is dependent on substrate thickness. In thismanner, any of the systems provided herein may include any of theabove-referenced pressure sensors for providing tactile information,such as a force applied to or from an external surface, including apressure that may spatially-vary over the contact area region of theapplied force.

There is tolerance with respect to the degree of alignment between theinner 610 and outer electronic devices 620, particularly as the systemsare readily calibrated by applying known forces or pressures andobserving the resultant change in capacitance (see, e.g., FIG. 6(d)),temperature or optical transmission. In an aspect, the substrate is atleast partially translucent or transparent to facilitate alignmentduring printing of the outer-facing electronic devices to the outersurface with the inner-facing electronic devices.

Use of aligned electrode array pairs provides arrays of capacitors,thereby allowing detection of a force or pressure distribution over thesurface of the system by virtue of spatially varying changes insubstrate thickness 630 that are detected by the different capacitors.

STATEMENTS REGARDING INCORPORATION BY REFERENCE AND VARIATIONS

All references throughout this application, for example patent documentsincluding issued or granted patents or equivalents; patent applicationpublications; and non-patent literature documents or other sourcematerial; are hereby incorporated by reference herein in theirentireties, as though individually incorporated by reference, to theextent each reference is at least partially not inconsistent with thedisclosure in this application (for example, a reference that ispartially inconsistent is incorporated by reference except for thepartially inconsistent portion of the reference).

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention inthe use of such terms and expressions of excluding any equivalents ofthe features shown and described or portions thereof, but it isrecognized that various modifications are possible within the scope ofthe invention claimed. Thus, it should be understood that although thepresent invention has been specifically disclosed by preferredembodiments, exemplary embodiments and optional features, modificationand variation of the concepts herein disclosed may be resorted to bythose skilled in the art, and that such modifications and variations areconsidered to be within the scope of this invention as defined by theappended claims. The specific embodiments provided herein are examplesof useful embodiments of the present invention and it will be apparentto one skilled in the art that the present invention may be carried outusing a large number of variations of the devices, device components,methods steps set forth in the present description. As will be obviousto one of skill in the art, methods and devices useful for the presentmethods can include a large number of optional composition andprocessing elements and steps.

When a group of substituents is disclosed herein, it is understood thatall individual members of that group and all subgroups, are disclosedseparately. When a Markush group or other grouping is used herein, allindividual members of the group and all combinations and subcombinationspossible of the group are intended to be individually included in thedisclosure. Specific names of compounds are intended to be exemplary, asit is known that one of ordinary skill in the art can name the samecompounds differently.

Every formulation or combination of components described or exemplifiedherein can be used to practice the invention, unless otherwise stated.

Whenever a range is given in the specification, for example, a physicalproperty range, a size range, a temperature range, a time range, or acomposition or concentration range, all intermediate ranges andsubranges, as well as all individual values included in the ranges givenare intended to be included in the disclosure. It will be understoodthat any subranges or individual values in a range or subrange that areincluded in the description herein can be excluded from the claimsherein.

All patents and publications mentioned in the specification areindicative of the levels of skill of those skilled in the art to whichthe invention pertains. References cited herein are incorporated byreference herein in their entirety to indicate the state of the art asof their publication or filing date and it is intended that thisinformation can be employed herein, if needed, to exclude specificembodiments that are in the prior art. For example, when composition ofmatter are claimed, it should be understood that compounds known andavailable in the art prior to Applicant's invention, including compoundsfor which an enabling disclosure is provided in the references citedherein, are not intended to be included in the composition of matterclaims herein.

As used herein, “comprising” is synonymous with “including,”“containing,” or “characterized by,” and is inclusive or open-ended anddoes not exclude additional, unrecited elements or method steps. As usedherein, “consisting of” excludes any element, step, or ingredient notspecified in the claim element. As used herein, “consisting essentiallyof” does not exclude materials or steps that do not materially affectthe basic and novel characteristics of the claim. In each instanceherein any of the terms “comprising”, “consisting essentially of” and“consisting of” may be replaced with either of the other two terms. Theinvention illustratively described herein suitably may be practiced inthe absence of any element or elements, limitation or limitations whichis not specifically disclosed herein.

One of ordinary skill in the art will appreciate that startingmaterials, biological materials, reagents, synthetic methods,purification methods, analytical methods, assay methods, and biologicalmethods other than those specifically exemplified can be employed in thepractice of the invention without resort to undue experimentation. Allart-known functional equivalents, of any such materials and methods areintended to be included in this invention. The terms and expressionswhich have been employed are used as terms of description and not oflimitation, and there is no intention that in the use of such terms andexpressions of excluding any equivalents of the features shown anddescribed or portions thereof, but it is recognized that variousmodifications are possible within the scope of the invention claimed.Thus, it should be understood that although the present invention hasbeen specifically disclosed by preferred embodiments and optionalfeatures, modification and variation of the concepts herein disclosedmay be resorted to by those skilled in the art, and that suchmodifications and variations are considered to be within the scope ofthis invention as defined by the appended claims.

The following patents and patent applications are hereby incorporated byreference in their entireties: U.S. Pat. Nos. 7,195,733; 7,622,367;7,557,367; 7,799,699; 7,943,491; 7,521,292; 8,367,035; 8,217,381;7,932,123; 7,972,875; 8,198,621; 7,704,684; 7,982,296; 8,039,847;7,705,280; 2010/0002402; 2010/0052112; 2010/0317132; 2012/0105528;2012/0157804; 2008/0055581; 2011/0230747; 2011/0187798; 2013/0072775;Ser. No. 13/624,096 (filed Sep. 21, 2012).

We claim:
 1. An appendage mountable electronic system, said systemcomprising: an elastomeric substrate having an inner surface and anouter surface, wherein the inner surface defines an enclosure capable ofreceiving an appendage having a curved surface, and the elastomericsubstrate has a resting thickness that is less than 10 mm; a firstelectronic device supported by the inner surface; a second electronicdevice supported by the outer substrate, wherein the first and secondelectronic devices are in an opposed configuration with respect to eachother and separated by a thickness of the elastomeric substrate to forma pressure sensor whose output varies as a function of elastomericsubstrate thickness; each of the first and second electronic devicescomprises one or more inorganic semiconductor components, one or moremetallic components, or one or more inorganic semiconductor componentsand one or more metallic components, having a thickness less than 1 mmand a lateral dimension less than 5 mm, having: a net bending stiffnessless that or equal to 1×10⁸GPa pm³; and/or a net flexural rigidity lessthan or equal to 1×10−⁴ Nm.
 2. The system of claim 1, wherein the sensoris a pressure sensor comprising a pair of spatially aligned electrodeswith a first electrode supported by the inner surface and a secondelectrode supported by the outer surface, wherein the pair of electrodesare in electrical communication with each other and having a capacitancebetween the pair of electrodes that varies with elastomeric substratethickness between the pair of electrodes.
 3. The system of claim 2,wherein an applied pressure to the elastomeric substrate decreasessubstrate thickness between the pair of electrodes, thereby increasingthe capacitance.
 4. The system of claim 2, comprising an array of firstelectrodes and an array of second electrodes, wherein the array of firstelectrodes and the array of second electrodes are spatially aligned witheach other to form an array of capacitors, each capacitor having a pairof electrodes separated by a thickness of the elastomeric substrate,each individual member of the array of capacitors having a capacitancethat independently varies as a function of the elastomeric substratethickness between the electrodes of the individual member of the arrayof capacitors.
 5. The system of claim 4, further comprising a firstplurality of electrical interconnects to electrically connect eachmember of the array of first electrodes and a second plurality ofelectrical interconnects to electrically connect each member of thesecond array of electrodes, wherein the electrical interconnects are ina serpentine configuration.
 6. The system of claim 5, wherein the firstplurality of electrical interconnects is encapsulated by a firstencapsulation layer supported by the elastomeric substrate inner surfaceand the second plurality of electrical interconnects is encapsulated bya second encapsulation layer supported by the elastomeric substrateouter layer.
 7. The system of claim 5, further comprising a barrierlayer to electrically isolate the first plurality of electricalinterconnects from the second plurality of electrical interconnects. 8.The system of claim 1, wherein the first and second electronic devicesare in thermal communication with each other, wherein one of theelectronic devices is a thermal source and the electronic device is athermal detector that measures a temperature, and a change inelastomeric substrate thickness between the thermal source and thethermal detector changes the temperature measured by the thermaldetector.
 9. The system of claim 1, wherein said system is stretchableand configured to conformally contact with a living tissue surfaceduring use.
 10. An appendage mountable electronic system, said systemcomprising: a flexible or stretchable substrate having an inner surfaceand an outer surface, wherein the inner surface defines an enclosurecapable of receiving an appendage having a curved surface; and aflexible or stretchable electronic device comprising one or moresensors, supported by the inner surface of said flexible or stretchablesubstrate; said sensors comprising one or more inorganic semiconductorcomponents, one or more metallic components, or one or more inorganicsemiconductor components and one or more metallic components; wherein atleast a portion of said inorganic semiconductor components, metalliccomponents or both have a thickness less than or equal to 500 microns;wherein said flexible or stretchable substrate and said electronicdevice provide a net bending stiffness of the system low enough suchthat the inner surface of the substrate is capable of establishingconformal contact with a surface of said appendage provided within saidenclosure during use, one or more actuators for tissue stimulation,wherein said one or more actuators are supported by the inner surface ofsaid flexible or stretchable substrate; said actuators comprising one ormore inorganic semiconductor components, one or more metalliccomponents, or one or more inorganic semiconductor components and one ormore metallic components; wherein at least a portion of said inorganicsemiconductor components, metallic components or both have a thicknessless than or equal to 500 microns.
 11. The system of claim 10 configuredfor mounting to a fingertip or any portion thereof.
 12. The system ofclaim 11, having a footprint surface area that is between 0.5 cm² and 2cm².
 13. The system of claim 11, that is incorporated into a glovefinger or a glove fingertip.
 14. The system of claim 10, wherein saidactuators comprise electrotactile stimulators and said sensors comprisetactile sensors.
 15. The system of claim 14, further comprising awireless transmitter for bi-directional communication between the systemand a virtual environment.
 16. The system of claim 10, wherein saidelectronic device comprises a stretchable or flexible electrode arraycomprising a plurality of electrodes, multiplex circuitry andamplification circuitry.
 17. The system of claim 10, wherein saidsensors comprise tactile sensors, motion sensors, temperature sensors,or any combination thereof.
 18. The system of claim 10, furthercomprising a wireless transmitter connected to said electronic device.19. The system of claim 10, further comprising a wireless power sourceconnected to said electronic device.
 20. The system of claim 1, whereinthe system is configured to adhere to a skin layer by van der Waalsinteractions during use.